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HURRICANE GERT
08-07-2017, 06:19 AM
Post: #11
RE: INVEST 99L
Look fishy and 90L is now Franklin that should not be a factor either zzzzzz

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08-07-2017, 02:25 PM
Post: #12
RE: INVEST 99L
Henson for JM


Quote: [Image: franklin-ir-1615Z-8.7.17-835px.jpg]


Tropical Storm Franklin Aims for Yucatan
Bob Henson · August 7, 2017, 17:56




Above: GOES-16 infrared satellite image of Hurricane Franklin as of 1615Z (12:15 pm EDT) Monday, August 7, 2017. GOES-16 data are preliminary and non-operational. Image credit: NASA/MSFC Earth Science Branch.

Steadily gathering strength in the northwest Caribbean, Tropical Storm Franklin is on course to strike the eastern coast of the Yucatan Peninsula on Monday night. Franklin could undergo a brief period of rapid intensification that makes it a hurricane just before landfall. At 11 am EDT Monday, a hurricane watch and a tropical storm warning were in effect for the Mexican coast from Chetumal to Punta Allen. Additional parts of the Yucatan coast of Mexico and Belize were under tropical storm watches or warnings.


After days as a loosely organized tropical wave rolling through the Caribbean, Franklin began consolidating on Sunday and became a tropical storm on Sunday night. At 2 pm EDT Monday, the NOAA/NWS National Hurricane Center was locating the center Franklin at about 185 miles east of Belize City, with top sustained winds up to 60 mph. A large shield of intense thunderstorms covered the area near and to the north and east of Franklin’s center, with increasing upper-level outflow evident on the fringes of this shield. A Hurricane Hunter flight found winds of 48 knots at flight level well northeast of Franklin’s center at 12:44 pm EDT Monday, with the center located just south of a small dry slot evident in satellite imagery.



[Image: franklin-viz-16Z-8.7.17.jpeg]
Figure 1. GOES-16 visible-wavelength satellite image of Hurricane Franklin as of 1600Z (noon EDT) Monday, August 7, 2017. Satellite loops show that the feature resembling an eye is most likely a dry slot wrapped just north of the main center of circulation, rather than a true eye. Image credit: NASA/MSFC Earth Science Branch.



Outlook for Franklin


Conditions are very supportive of further growth in the few hours before Franklin makes landfall on Monday night, especially now that the storm is organized enough to take advantage of the favorable set-up. Wind shear will drop below 10 knots by Monday afternoon, according to 12Z Monday output from the SHIPS statistical model. Sea surface temperatures of 29-30°C (84-86°F) are about 1°C above average for this time of year, and Franklin is passing across an area of deep oceanic heat content, which lowers the odds that strong winds will bring cooler water to the surface.



[Image: oceanic-heat-8.6.17.jpg]
Figure 2. Tropical cyclone heat potential (TCHP) across the Caribbean Sea as of Sunday, August 6, 2017, in kilojoules per square centimeter. TCHP integrates the amount of heat through the depth of the upper ocean as measured by temperatures at each level. The red and white zone across the northwest Caribbean is associated with hurricane-supportive water temperatures of at least 26°C (79°F) that extend more than 125 meters (410 feet) deep. Image credit: NOAA/AOML.

Although it is not shown in the official NHC forecast (Figure 3 below), it is quite possible that Franklin will become a Category 1 hurricane just before landfall, between the forecast points at 7 pm EDT Monday and 7 am EDT Tuesday. If so, it will be the first Atlantic hurricane of 2017. In records going back to 1851, only four other years have seen six Atlantic tropical storms or hurricanes by August 6, according to Phil Klotzbach (Colorado State University). Those years are 1936, 1959, 2005, and 2012.


Torrential rain should be the main threat from Franklin, although gale-force winds may extend more than 100 miles up the coast from where Franklin makes landfall on the Yucatan Peninsula.




[Image: wu-tracking-franklin-15Z-8.7.17-640px.jpg]
Figure 3. WU depiction of the official NHC forecast for Franklin as of 11:00 am EDT Monday, August 7, 2017.

Computer models are in very close agreement on Franklin’s track, which will make a gentle leftward arc across the Yucatan Peninsula and the Bay of Campeche. Franklin will exit the peninsula in a weakened state, though still likely a tropical storm. Although it is not shown on the tracking map—because it would occur between forecast points—Franklin may have a second brief chance at rapid intensification to hurricane strength just before it makes landfall on the northeast coast of Mexico well south of Tampico. The concave topography of the Bay of Campeche helps impart spin to tropical cyclones, and water temperatures will again be very warm, although the oceanic heat content is less than in the northwest Caribbean.


The last several runs of the HWRF model—our best short-term guidance for tropical cyclone intensity—has been consistent in bringing Franklin to northeast Mexico late Wednesday night as a Category 1 hurricane.



A good analog for Franklin is 2012’s Hurricane Ernesto, which became a tropical storm several days before approaching the Yucatan on a very similar track to Franklin’s—and on the same day of the year to boot (see embedded tweet below from Brian McNoldy). Ernesto quickly strengthened to Category 2 intensity just before landfall on the coast of Mahahual, Mexico. Ernesto failed to regain hurricane status after passing over the Bay of Campeche, but Franklin’s track is expect to be far enough north of Ernesto’s to give it more time over the bay’s warm waters without direct interference from land.

[Image: ir-99L-1645Z-8.7.17-720px.jpg]
Figure 4. Enhanced infrared image of Invest 99L as of 1645Z (12:45 pm EDT) Monday, August 7, 2017. Image credit: NOAA/NESDIS.


99L: No worries for the time being

The long-struggling tropical wave in the central Atlantic known as Invest 99L continues to persevere, but its long-term future remains highly uncertain. Dry air from the Saharan Air Layer, and moderate to strong wind shear of 10-20 knots, have taken a toll on the disorganized showers and thunderstorms (convection) around 99L’s weak, elongated center, which is located midway between the Cape Verde islands and the Lesser Antilles. There were some hints of a more centralized convective pattern developing in satellite imagery on Monday (see Figure 4). We'll see if this apparent trend continues with the approach of nighttime, when convection over the tropics typically reaches a diurnal peak.


Wind shear and dry air will continue to plague the resilient 99L for at least the next several days. The wave is moving toward warmer sea surface temperatures, and it could hang together long enough for a renewed chance at intensification once it reaches the area near or north of the Lesser Antilles. Overall, though, models have pulled back on the idea of long-term strengthening of 99L. Between 10% and 20% of the European ensemble members from Sunday evening indicate that 99L could yet become a tropical storm late this week or even early next week, potentially heading toward the U.S. East Coast more than a week from now. Only 1 of 20 GFS ensemble members bring 99L to tropical storm strength, and all of those members dissipate the system before it could get as far west as Puerto Rico. None of the three most reliable long-term models—the GFS, Euro, and UKMET—developed 99L in their operational runs from Sunday night.


In its 2:00 pm EDT Monday tropical weather outlook, NHC gave 99L a near-zero chance of becoming at least a tropical depression by Wednesday and a 20% chance through Saturday.


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08-08-2017, 07:59 PM
Post: #13
RE: INVEST 99L
ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 PM EDT Tue Aug 8 2017

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

The National Hurricane Center is issuing advisories on Tropical
Storm Franklin, located off the west coast of the Yucatan peninsula.

1. A trough of low pressure located about 650 miles east of the
Leeward Islands continues to produce disorganized showers and
thunderstorms. Environmental conditions are expected to remain
unfavorable for significant development during the next couple of
days. However, environmental conditions are forecast to become
a little more conducive for development late this week while the
system moves generally west-northwestward at about 15 mph over the
western Atlantic.
* Formation chance through 48 hours...low...near 0 percent.
* Formation chance through 5 days...medium...40 percent.

Forecaster Brown
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08-09-2017, 12:41 PM (This post was last modified: 08-09-2017 12:42 PM by Her-icane.)
Post: #14
RE: INVEST 99L
JM


Quote: [Image: franklin-sat-aug9.jpeg]


Franklin Nears Hurricane Strength as it Approaches Mexico
Dr. Jeff Masters · August 9, 2017, 16:16




Above: Tropical Storm Franklin as seen at 12:07 pm EDT August 9, 2017. At the time. Franklin had top winds of 70 mph. Image credit: NASA/GSFC.


Tropical Storm Franklin is steadily intensifying over the hurricane-friendly waters of Mexico’s Bay of Campeche, and is expected to be a Category 1 hurricane with top winds near 85 mph when it makes landfall in the Veracruz state of Mexico, about 70 miles north-northwest of the city of Veracruz, late Wednesday night. Satellite images on Wednesday afternoon showed that Franklin was an averaged-sized tropical storm, with plenty of heavy thunderstorms that filled most of Mexico’s Bay of Campeche. A large rain band was already bringing torrential rains to much of the coast in the warned area. Conditions were favorable for intensification, with sea surface temperatures (SSTs) near 30°C (86°F), plenty of moisture (a mid-level relative humidity near 70%), and moderate wind shear of 15 knots. An Air Force hurricane hunter aircraft penetrated into Franklin's eye at 12:42 pm EDT Wednesday, and found the central pressure was 985 mb--the same as the pressure from NHC's 11 am EDT Wednesday advisory. Radar from a NOAA hurricane hunter aircraft earlier this morning showed that Franklin had not yet built a well-defined eyewall, but the 12:42 pm EDT Wednesday eye report from the Air Force plane reported that Franklin had indeed built a full eyewall, with an elliptical-shaped eye 40 miles long by 20 miles wide.



[Image: franklin-rain-fct.jpg]
Figure 1. Rainfall forecast for Franklin from the RPM model for the period ending 1 pm CDT Thursday (Jueves), August 10, 2017. Image credit: CONAGUA.



Forecast for Franklin



There’s not much time for intensification of Franklin beyond Category 1 status, and the storm is primarily a heavy rainfall threat for Mexico, with widespread rain amounts of 4 – 8” expected. Franklin should have a lower impact than the last hurricane to hit the state of Veracruz, Hurricane Karl, whose eye crossed the coast about 10 miles north of Veracruz on September 17, 2010. Karl was the only major hurricane ever recorded in the Bay of Campeche (south of 21° N latitude), and peaked as a Category 3 storm with 125 mph winds, about 5 hours before landfall. Karl brought a large area of 10 – 15” rainfall amounts to the northwestern half of the state of Veracruz. AIR Worldwide estimated total damage costs in Mexico at $206 million, and Karl killed 22 people. Karl did not get its name retired.





Invest 99L not a threat to land areas


An area of low pressure (99L) located about 400 miles east of the northern Lesser Antilles Islands at 8 am EDT Wednesday was headed west-northwest to northwest at about 10 mph. Satellite images on Wednesday afternoon showed that 99L had only a sparse amount of heavy thunderstorm activity, but a modest degree of spin. The atmosphere surrounding the disturbance was quite dry, with a mid-level relative humidity around 45%.


The 12Z Wednesday run of the SHIPS modelpredicted that wind shear would drop to the low range, less than 10 knots, on Friday and Saturday, when 99L was expected to be a few hundred miles north of the Lesser Antilles Islands. However, the atmosphere was predicted be very dry at that time, potentially limiting development--unless 99L can carve out a protective “pouch” of moisture to stave off the dryness.


By Sunday, 99L should find a moister atmosphere with mid-level relative humidity around 60%, though wind shear is predicted to rise to a moderately high 15 – 20 knots by then. Sea surface temperatures will be plenty warm enough for development, around 29°C (84°F)--about 1°C above average for this time of year. The 0Z Wednesday European model ensemble forecast had 46% of its members bringing 99L between North Carolina and Bermuda as a tropical storm early next week. However, our other two reliable models for predicting tropical cyclone genesis, the GFS and UKMET models, did not show development of 99L in their 0Z Wednesday runs. The 12Z Wednesday run of the GFS also showed no development, though the 12Z Wednesday run of the UKMET did show some weak development early next week.


If it does manage to develop, 99L will be steered by a large and strong Atlantic ridge extending west toward the mid-Atlantic coast. The predicted shape of the ridge, and the projected approach of a strong upper-level trough across the Northeast U.S., suggests that 99L will recurve to the north and north-northeast between North Carolina and Bermuda, sparing those locations any direct impacts. In its 8 am Wednesday tropical weather outlook, the NOAA/NWS National Hurricane Center gave 99L a near-zero chance of developing into at least a tropical depression by Friday morning, but a 40% chance by Monday morning.
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08-10-2017, 06:27 PM
Post: #15
RE: INVEST 99L
JM


Quote: [Image: franklin-boat.jpg] Hurricane Franklin


Dissipates Over Mexico; 99L May Develop

Dr. Jeff Masters · August 10, 2017, 16:05

Above: Fishermen push a boat out of the sea in anticipation of the arrival of Tropical Storm Franklin in the port city of Veracruz in Veracruz state, Mexico on August 9, 2017. Image credit: VICTORIA RAZO/AFP/Getty Images.

Hurricane Franklin dissipated over the rugged terrain of central Mexico east of Mexico City on Thursday morning, after making landfall at 1 am EDT Thursday, August 10, in the Veracruz state of Mexico, about 70 miles north of the city of Veracruz. Franklin became the first Atlantic hurricane of 2017 at 5 pm EDT August 9. This formation date is just one day earlier than the average August 10 formation date of the season’s first hurricane. At landfall, Franklin was at peak intensity--a Category 1 hurricane with 85 mph winds.



[Image: franklin-modis-aug9.jpeg]Figure 1. MODIS true-color satellite image of Franklin, taken at 2:54 pm EDT August 9, 2017. At the time, Franklin was a tropical storm with 70 mph sustained winds, and would be upgraded to a hurricane two hours later. Image credit: NASA.

Impact of Franklin


Franklin should end up dumping widespread rain amounts of 4 – 8” along its track, resulting in a less severe impact than the last hurricane to hit the state of Veracruz, Hurricane Karl. Karl crossed the coast about 10 miles north of Veracruz on September 17, 2010, bringing a large area of 10 – 15” rainfall amounts to the northwestern half of the state of Veracruz. Karl was the only major hurricane ever recorded in the Bay of Campeche (south of 21° N latitude), and peaked as a Category 3 storm with 125 mph winds, about 5 hours before landfall. AIR Worldwide estimated total damage costs in Mexico at $206 million, and Karl killed 22 people. Karl did not get its name retired.



Franklin’s remains could regenerate over the Pacific

Satellite images on Thursday morning showed that the remains of Franklin were bringing heavy rains to much of south-central Mexico, and were headed westwards at 20 mph. Franklin’s remains will emerge over the Pacific Ocean on Friday, when regeneration into a tropical depression may occur, as predicted by both the 0Z and 6Z Thursday runs of the GFS model. The European model was more ambivalent about regeneration, but did show some reorganization would occur this weekend. In their 8 am Thursday tropical weather outlook, the National Hurricane Center gave the remains of Franklin a 20% chance of redeveloping over the Pacific by Saturday morning, and a 40% chance by Tuesday morning. The storm is expected to move west-northwest, passing several hundred miles south of the southern tip of Mexico’s Baja Peninsula early next week. Since Franklin did not survive the crossing of Mexico as an identifiable tropical cyclone, the new storm would get a new Eastern Pacific name. The next named storm in the list is Jova. By early next week, any potential Tropical Storm Jova will encounter a less conducive atmosphere for development, and it is unlikely that we will see a Hurricane Jova.


As documented by The Weather Company’s Jon Erdman in his Thursday morning post, a similar scenario happened almost exactly one year ago, also resulting in an eastern Pacific "J" storm. Hurricane Earl made landfall in Belize on Aug. 4, 2016, and less than 24 hours after Earl dissipated, a tropical depression formed from the remnants of Earl. This storm went on to develop into Tropical Storm Javier. Since the mid-1960s, when satellite surveillance of the tropics became routine, the remnants of tropical cyclones crossing from one ocean basin to the other and reforming has occurred every 3 to 4 years.



[Image: viz-99L-1530Z-8.10.17.jpg]
Figure 2. Visible-wavelength GOES-16 satellite image of Invest 99L as of 1530Z (11:30 am EDT) Thursday, August 20, 2017. GOES-16 images are preliminary and non-operational. Image credit: RAMMB/CIRA/CSU.

99L may yet develop this weekend

It’s been a fighter, but the never-say-die tropical wave known as Invest 99L continues to face long odds. The resilient system may have its last, best shot at development this weekend, though. Located several hundred miles northeast of the Virgin islands on Thursday morning, 99L maintained a small core of showers and thunderstorms (convection) through Wednesday night. The convection was not intense or very well structured, and it was mostly east of the ill-defined center of 99L, but it was expanding in area on Thursday morning. Relentless wind shear—on the order of 20-25 knots on Thursday morning—is projected in the 12Z Thursday SHIPS model output to decrease to a more moderate 10-15 knots on Friday and Saturday, before again increasing on Sunday and Monday to around 20 knots. Mid-level relative humidity around 99L is also projected to increase, to around 50-55% this weekend, and sea surface temperatures of around 29°C will be more than adequate for development. In its 8 AM Thursday tropical weather outlook, NHC gave 99L a 20% chance of development into at least a depression by Saturday and a 40% chance by Tuesday.


The European model has pulled back on its bullish outlook for 99L after most of its ensemble members a day before had developed the system into a tropical storm or hurricane. About 2/3 of the 00Z Thursday Euro ensemble members create a tropical depression out of 99L by Friday evening. However, less than 10% bring the system to tropical storm strength, and only one of the 50 members creates a long-track tropical storm that recurves off the East Coast. None of the GFS ensemble members from 00Z Thursday develops 99L at all, and the same is true in the 00Z Thursday operational runs from our three top global models for tropical cyclone development: the Euro, GFS, and UKMET.



Elsewhere in the tropics

A new wave coming off Africa early next week will bear watching as we approach the peak of the Cape Verde season, when the Main Development Region (MDR) between Africa and the Lesser Antilles is at its most active. About 30% of Euro and 20% of GFS ensemble members bring this wave to at least tropical depression strength next week, as it heads west-northwest across the MDR on a track that could end up similar to 99L’s.


The Madden-Julian Oscillation should be in a mode that favors development in the Atlantic during mid- to late August, based on the latest NOAA forecasts of rising and sinking air at upper levels.


In the Eastern Pacific, there is the chance that the remnants of Franklin will redevelop (as discussed above), and another tropical low is expected to take shape early next week further to the south. NHC gave that system a 40% chance of development through Tuesday in its Thursday morning outlook.
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08-11-2017, 07:14 PM (This post was last modified: 08-11-2017 08:07 PM by Her-icane.)
Post: #16
RE: INVEST 99L
ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 PM EDT Fri Aug 11 2017

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

1. Showers and thunderstorms associated with a broad area of low
pressure located about 300 miles east of the Turks and Caicos
Islands have changed little in organization since this morning.
Dry air aloft and unfavorable upper-level winds have limited
significant development during the past few days. Environmental
conditions, however, are expected to become a little more conducive
for development during the next day or two, and this system could
become a tropical depression over the weekend. The low is forecast
to move generally northwestward through the weekend and is likely
to turn northeastward away from the United States early next week.
* Formation chance through 48 hours...medium...40 percent.
* Formation chance through 5 days...medium...60 percent.

Forecaster Brown

Henson for JM

Quote: [Image: viz-99L-1530Z-8.11.17-835px.jpg] Invest 99L May Develop; Not a Threat to Land

Bob Henson · August 11, 2017, 16:22






Above: Visible-wavelength satellite image of Invest 99L as of 1530Z (11:30 am EDT) Friday, August 11, 2017. Image credit: RAMMB/CIRA/CSU.

An area of low pressure (99L) located about 200 miles north of the northern Lesser Antilles Islands at 8 am EDT Friday was headed west-northwest to northwest at about 10 mph. Satellite images on Friday morning showed that 99L had only a sparse amount of heavy thunderstorm activity, but a modest degree of spin. The atmosphere surrounding the disturbance was dry, with a mid-level relative humidity around 50%. This dry air was the primary impediment to development, since sea surface temperatures were warm, at 29°C (84°F), and wind shear was moderate, 10 – 20 knots.


The 12Z Friday run of the SHIPS modelpredicted that wind shear would drop to the low range, less than 10 knots, on Friday afternoon through Saturday night, which should allow the storm to increase in organization--though the surrounding atmosphere will remain dry. On Sunday and Monday, though, wind shear is predicted to rise to a high 20 - 25 knots, which will make further development difficult. Sea surface temperatures will remain around 29°C (84°F).


[Image: gfs-700-400rh-12Z-8.11.17_0.jpg]
Figure 1. The area of moisture associated with 99L, located northeast of Puerto Rico, was surrounded by drier air on Friday morning, August 11. This map shows the starting-point analysis in the GFS model at 12Z (8:00 am EDT) Friday. Green and brown colors (legend at right) show relative humidity in the layer between 700 and 400 mb, or between about 10,000 and 24,000 feet. Average winds through the same layer are shown by wind flags and barbs. Image credit: tropicaltidbits.com.

Model support for development of 99L is lukewarm. The 0Z Friday European model ensemble forecast had 38% of its members bringing 99L to tropical storm status early next week, and the UKMET model showed some limited development of 99L early next week. However, our other model for predicting tropical cyclone genesis, the GFS, did not show development of 99L in its 0Z and 06Z Friday runs.


If it does manage to develop, 99L is not expected to directly threaten any land areas. A trough of low pressure pushing off the U.S. East Coast will pull 99L to the north and then northeast, with the storm passing between North Carolina and Bermuda, then well south of the Canadian Maritime Provinces. In its 8 am Friday tropical weather outlook, the National Hurricane Center gave 99L a 30% chance of developing into at least a tropical depression by Sunday morning, and a 50% chance by Wednesday morning. The next name on the Atlantic list of storms is Gert.


Franklin’s remains regenerating over the Pacific


Satellite images on Friday morning showed that the remains of Hurricane Franklin, which hit the Veracruz state of Mexico early Friday morning, were over the Pacific Ocean over 500 miles south-southwest of the tip of the Baja Peninsula. The disturbance, dubbed 92E by NHC, was well-organized, with plenty of spin and heavy thunderstorms. In their 8 am Friday tropical weather outlook, the National Hurricane Center gave the remains of Franklin a 90% chance of developing into a tropical depression by Sunday. The storm is expected to move west-northwest, passing several hundred miles south of the southern tip of Mexico’s Baja Peninsula. Since Franklin did not survive the crossing of Mexico as an identifiable tropical cyclone, the new storm would get a new Eastern Pacific name. The next named storm in the list is Jova. Any potential Tropical Storm Jova will encounter a less conducive atmosphere for development by Monday, and it is unlikely that we will see a Hurricane Jova.


[Image: ir-ne-pac-16Z-8.11.17.jpg]
Figure 2. Infrared satellite image of the remnants of Hurricane Franklin reorganizing in the northeast Pacific off the Mexican coast at 1600Z (noon EDT) Friday, August 11, 2017. Image credit: NASA/MSFC Earth Science Branch.

Elsewhere in the tropics


A weak and elongated area of low pressure just off the east coast of Florida on Friday morning was accompanied by disorganized showers and thunderstorms extending from southern Florida northeastward across the southwestern Atlantic. Dry air and high wind shear of 30 knots are expected to keep this system from developing, but it could still produce locally heavy rains to portions of the Florida peninsula as it moves northward during the weekend. In its 8 am Friday tropical weather outlook, the National Hurricane Center gave the system 2-day and 5-day odds of development of 10%.


A new tropical wave expected to come off the coast of Africa on Sunday will bear watching as we approach the peak of the Cape Verde season, when the Main Development Region (MDR) between Africa and the Lesser Antilles is at its most active. However, this wave had lower model support for development on Friday morning compared to Thursday morning—less than 10% of the 70 members of the European and GFS models predicted development in their 0Z Friday runs, compared to 20 – 30% predicting development in their 0Z Thursday forecasts. The wave will head west to west-northwest across the MDR on a track that could end up similar to 99L’s, passing near or a few hundred miles north of the northern Lesser Antilles Islands about a week after emerging from Africa.


The Madden-Julian Oscillation should be in a mode that favors development in the Atlantic during mid- to late August, based on the latest NOAA forecasts of rising and sinking air at upper levels.

Henson for JM


Quote: [Image: viz-99L-1530Z-8.11.17-835px.jpg] Invest 99L May Develop; Not a Threat to Land


Bob Henson · August 11, 2017, 16:22






Above: Visible-wavelength satellite image of Invest 99L as of 1530Z (11:30 am EDT) Friday, August 11, 2017. Image credit: RAMMB/CIRA/CSU.


An area of low pressure (99L) located about 200 miles north of the northern Lesser Antilles Islands at 8 am EDT Friday was headed west-northwest to northwest at about 10 mph. Satellite images on Friday morning showed that 99L had only a sparse amount of heavy thunderstorm activity, but a modest degree of spin. The atmosphere surrounding the disturbance was dry, with a mid-level relative humidity around 50%. This dry air was the primary impediment to development, since sea surface temperatures were warm, at 29°C (84°F), and wind shear was moderate, 10 – 20 knots.


The 12Z Friday run of the SHIPS modelpredicted that wind shear would drop to the low range, less than 10 knots, on Friday afternoon through Saturday night, which should allow the storm to increase in organization--though the surrounding atmosphere will remain dry. On Sunday and Monday, though, wind shear is predicted to rise to a high 20 - 25 knots, which will make further development difficult. Sea surface temperatures will remain around 29°C (84°F).


[Image: gfs-700-400rh-12Z-8.11.17_0.jpg]
Figure 1. The area of moisture associated with 99L, located northeast of Puerto Rico, was surrounded by drier air on Friday morning, August 11. This map shows the starting-point analysis in the GFS model at 12Z (8:00 am EDT) Friday. Green and brown colors (legend at right) show relative humidity in the layer between 700 and 400 mb, or between about 10,000 and 24,000 feet. Average winds through the same layer are shown by wind flags and barbs. Image credit: tropicaltidbits.com.


Model support for development of 99L is lukewarm. The 0Z Friday European model ensemble forecast had 38% of its members bringing 99L to tropical storm status early next week, and the UKMET model showed some limited development of 99L early next week. However, our other model for predicting tropical cyclone genesis, the GFS, did not show development of 99L in its 0Z and 06Z Friday runs.


If it does manage to develop, 99L is not expected to directly threaten any land areas. A trough of low pressure pushing off the U.S. East Coast will pull 99L to the north and then northeast, with the storm passing between North Carolina and Bermuda, then well south of the Canadian Maritime Provinces. In its 8 am Friday tropical weather outlook, the National Hurricane Center gave 99L a 30% chance of developing into at least a tropical depression by Sunday morning, and a 50% chance by Wednesday morning. The next name on the Atlantic list of storms is Gert.


Franklin’s remains regenerating over the Pacific

Satellite images on Friday morning showed that the remains of Hurricane Franklin, which hit the Veracruz state of Mexico early Friday morning, were over the Pacific Ocean over 500 miles south-southwest of the tip of the Baja Peninsula. The disturbance, dubbed 92E by NHC, was well-organized, with plenty of spin and heavy thunderstorms. In their 8 am Friday tropical weather outlook, the National Hurricane Center gave the remains of Franklin a 90% chance of developing into a tropical depression by Sunday. The storm is expected to move west-northwest, passing several hundred miles south of the southern tip of Mexico’s Baja Peninsula. Since Franklin did not survive the crossing of Mexico as an identifiable tropical cyclone, the new storm would get a new Eastern Pacific name. The next named storm in the list is Jova. Any potential Tropical Storm Jova will encounter a less conducive atmosphere for development by Monday, and it is unlikely that we will see a Hurricane Jova.


[Image: ir-ne-pac-16Z-8.11.17.jpg]
Figure 2. Infrared satellite image of the remnants of Hurricane Franklin reorganizing in the northeast Pacific off the Mexican coast at 1600Z (noon EDT) Friday, August 11, 2017. Image credit: NASA/MSFC Earth Science Branch.

Elsewhere in the tropics


A weak and elongated area of low pressure just off the east coast of Florida on Friday morning was accompanied by disorganized showers and thunderstorms extending from southern Florida northeastward across the southwestern Atlantic. Dry air and high wind shear of 30 knots are expected to keep this system from developing, but it could still produce locally heavy rains to portions of the Florida peninsula as it moves northward during the weekend. In its 8 am Friday tropical weather outlook, the National Hurricane Center gave the system 2-day and 5-day odds of development of 10%.


A new tropical wave expected to come off the coast of Africa on Sunday will bear watching as we approach the peak of the Cape Verde season, when the Main Development Region (MDR) between Africa and the Lesser Antilles is at its most active. However, this wave had lower model support for development on Friday morning compared to Thursday morning—less than 10% of the 70 members of the European and GFS models predicted development in their 0Z Friday runs, compared to 20 – 30% predicting development in their 0Z Thursday forecasts. The wave will head west to west-northwest across the MDR on a track that could end up similar to 99L’s, passing near or a few hundred miles north of the northern Lesser Antilles Islands about a week after emerging from Africa.


The Madden-Julian Oscillation should be in a mode that favors development in the Atlantic during mid- to late August, based on the latest NOAA forecasts of rising and sinking air at upper levels.
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08-12-2017, 08:44 AM (This post was last modified: 08-12-2017 08:54 AM by Her-icane.)
Post: #17
RE: INVEST 99L
ZCZC MIATWOAT ALL
TTAA00 KNHC DDHHMM

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
800 AM EDT Sat Aug 12 2017

For the North Atlantic...Caribbean Sea and the Gulf of Mexico:

1. A low pressure area located about 150 miles northeast of the Turks
and Caicos Islands has become a little better defined this morning
and the shower activity has increased somewhat since yesterday.
Conditions are gradually becoming more conducive for development,
and a tropical depression could form during the next day or two. The
low is forecast to move northwestward and then northward through the
weekend, and then turn to the northeast away from the United States
early next week.
* Formation chance through 48 hours...medium...60 percent.
* Formation chance through 5 days...high...70 percent.

Forecaster Avila



000
NOUS42 KNHC 111344
REPRPD
WEATHER RECONNAISSANCE FLIGHTS
CARCAH, NATIONAL HURRICANE CENTER, MIAMI, FL.
0945 AM EDT FRI 11 AUGUST 2017
SUBJECT: TROPICAL CYCLONE PLAN OF THE DAY (TCPOD)
VALID 12/1100Z TO 13/1100Z AUGUST 2017
TCPOD NUMBER.....17-072

I. ATLANTIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. OUTLOOK FOR SUCCEEDING DAY: POSSIBLE LOW LEVEL INVEST
NEAR 29.0N 73.5W AT 13/1900Z.



II. PACIFIC REQUIREMENTS
1. NEGATIVE RECONNAISSANCE REQUIREMENTS.
2. SUCCEEDING DAY OUTLOOK.....NEGATIVE.

$$
JWP

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08-13-2017, 06:07 AM
Post: #18
RE: INVEST 99L
TD#8


Quote: Tropical Depression Eight Discussion Number 2
NWS National Hurricane Center Miami FL AL082017
500 AM EDT Sun Aug 13 2017

Satellite-derived winds from ASCAT passes at 0122Z and 0208Z
indicated that the tropical depression had a closed surface
circulation with peak winds of 33 kt in the southeastern quadrant.
However, those peak winds were occurring in the same area of the
circulation where NOAA Buoy 41046, which several hours ago measured
a sustained wind of 35 kt and a peak gust to 43 kt, due to what
appears to have been cold, downdraft-driven wind gusts based on a
sharp decrease in the temperature and dew point values. As a result,
the intensity will be held at 30 kt for this advisory, in line with
a consensus 30-kt estimate from TAFB, SAB, and UW-CIMSS ADT.

The initial motion estimate is 335/12 kt. The depression is forecast
to move north-northwestward to northward for the next 36 h around
the western portion a deep-layer subtropical ridge that is oriented
east-west along 30-32N latitude. By 48 h and beyond, a vigorous
shortwave trough currently located over the northern Plains is
expected to dig east-southeastward and weaken the ridge along the
east coast of the United States from the Carolinas northward to New
England. The increasing southwesterly flow ahead of the trough is
forecast to accelerate the cyclone northeastward, on an optimal
track about midway from the U.S. and Bermuda and keeping it away
from those two land masses. The new NHC tack forecast is similar
to the previous advisory, and lies close to a blend of the HCCA and
TVCN consensus track models.

The depression is expected to remain in a relatively low vertical
wind shear environment for the next 24-36 hours, but also within a
fairly dry mid-level moisture environment for the duration of the
forecast. As a result, only modest strengthening is expected during
the next couple of days. By 48 h and beyond, southwesterly vertical
wind shear is expected to steadily increase to more than 20 kt ahead
of the aforementioned shortwave trough, reaching 40-50 kt by 96-120
h, which should act to cap any additional intensification. Owing to
the strong shear, the cyclone is forecast to become extratropical by
days 4 and 5. The official intensity forecast is similar to the
previous advisory, and lies close to the consensus models IVCN and
ICON. The intensity forecast at 96 and 120 h reflects guidance
provided by the NOAA Ocean Prediction Center.

FORECAST POSITIONS AND MAX WINDS

INIT 13/0900Z 26.5N 70.9W 30 KT 35 MPH
12H 13/1800Z 28.1N 71.7W 35 KT 40 MPH
24H 14/0600Z 29.9N 72.2W 40 KT 45 MPH
36H 14/1800Z 31.5N 72.0W 45 KT 50 MPH
48H 15/0600Z 33.4N 71.0W 50 KT 60 MPH
72H 16/0600Z 37.7N 64.1W 50 KT 60 MPH
96H 17/0600Z 42.4N 50.8W 45 KT 50 MPH...POST-TROP/EXTRATROP
120H 18/0600Z 46.3N 36.5W 45 KT 50 MPH...POST-TROP/EXTRATROP

$$
Forecaster Stewart

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08-13-2017, 06:48 AM
Post: #19
RE: TD#8
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[Image of probabilities of 34-kt winds]
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08-13-2017, 02:10 PM
Post: #20
RE: TD#8
Henson for JM

Quote: [Image: td8-aug13-835px.jpg] Tropical Depression Eight Forms, But Not a Threat to Land

Bob Henson · August 13, 2017, 17:08


Above: Tropical Depression Eight as seen by the GOES-16 satellite at 10:30 am EDT August 13, 2017. Image credit: NOAA/CIRA/RAMMB. NOAA’s GOES-16 satellite has not been declared operational and its data are preliminary and undergoing testing.

Tropical Depression Eight (TD 8) formed on Saturday evening in the Atlantic waters between the Lesser Antilles Islands and Bermuda, and is likely to become the seventh named storm of the season--Tropical Storm Gert--by Monday. TD 8 is not expected to be a threat to any land areas, and no Hurricane Hunter flights were scheduled into TD 8 as of midday Sunday.


Satellite images late Sunday morning showed that the heavy thunderstorm activity associated with Tropical Depression Eight was limited primarily to the east side of the circulation, thanks to dry air interference. The system was embedded in an environment of very dry air with a relative humidity at mid-levels of the atmosphere near 45%. Otherwise, conditions were favorable for development, with low wind shear of 5 – 10 knots and warm sea surface temperatures of 29°C (84°F.) TD 8 was fairly symmetric with respectable upper-level outflow developing, and could well be a strong tropical storm by Tuesday.


The seventh named storm of the Atlantic hurricane season occurs, on average, on September 16, so we are seeing a lot of early-season activity this year. The record earliest seventh Atlantic named storm was 2005’s version of Tropical Storm Gert, which got its name on July 24 of that year.


Forecast for TD 8

The 12Z Sunday SHIPS model predicted that wind shear over TD 8 would mostly be in the moderate range, 10 – 20 knots, through Tuesday, which should allow TD 8 to intensify into Tropical Storm Gert. By Wednesday, the storm will begin encountering very high levels of wind shear above 30 knots, which should kill the system by Thursday or Friday. The models are in excellent agreement in a track arcing to the north then northeast early this week, taking TD 8 midway between North Carolina and Bermuda, then out to sea well south of the Canadian Maritime Provinces.
.


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