RE: HURRICANE MATTHEW
Quote: Hurricane Matthew Is Born in Caribbean; Uncertainty Reigns in Long-Term Outlook
By:Bob Henson , 10:06 PM GMT on September 29, 2016
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The 13th named storm of the 2016 Atlantic season became Hurricane Matthew at 2:00 pm EDT Thursday. After detecting a small area of hurricane-force winds earlier in the day, an Air Force Hurricane Hunter flight found more consistent evidence of surface winds up to the 75-mph hurricane threshold, thus prompting the upgrade. This is the first Matthew to reach hurricane strength since the name was introduced in 2004, and it’s also the fifth hurricane of the 2016 Atlantic season. Most of this year’s storms have been on the weak side, together producing only about 70% of the usual amount of accumulated cyclone energy for this point in the season. Matthew could boost that percentage considerably over the next week or more.
Figure 1. Satellite image for Matthew as of 5:07 pm EDT Thursday, September 26, 2016.
Fighting and surviving headwinds
Tropical cyclones often weaken or fail to develop in the “hurricane graveyard” of the eastern Caribbean Sea. Trade winds typically accelerate through the region in a way that leads to sinking air and enhanced vertical wind shear. (See details in this 2010 paper from the Bulletin of the American Meteorological Society). Indeed, Matthew has been fighting vertical wind shear of close to 20 knots that was predicted by some but not all models. Early Thursday, Matthew’s low-level center decoupled from its central convection (showers and thunderstorms) and was clearly visible on satellite. A new batch of convection erupted by midday Thursday atop the low-level center, and the old convection has morphed into a banding feature feeding into Matthew. These elements should help sustain and nourish Matthew’s growth. At the same time, Matthew is plowing into fairly dry air at middle levels of the atmosphere, as revealed in visible satellite imagery that shows low-level outflow features to the west of the center. Matthew’s sustained winds remained at 75 mph in the 5 pm EDT update from the National Hurricane Center. Radiometer observations from the midday Hurricane Hunter flight detected peak surface winds of up to 67 knots (77 mph) around 17Z (1:00 pm EDT).
A Tropical Storm Watch is in effect for the southeast Caribbean islands of Bonaire, Curacao, and Aruba as Matthew passes to the north. In addition, a rare Tropical Storm Watch is now in effect for the coast of Colombia, extending from the Venezuala border west to Riohacha. Matthew is not expected to make landfall in South America, but its large circulation could bring gales and heavy rains near the coast.
Figure 2. Vertical wind shear across the Caribbean as of 18Z (2:00 pm EDT) Thursday, September 29, 2016. Higher shear (unfavorable for tropical cyclones) is shown in red. Matthew has reached and maintained hurricane strength despite wind shear of around 20 knots. The shear may continue for another couple of days as Matthew enters the central Caribbean, but then is predicted to lessen. Image credit: CIMSS/University of Wisconsin/SSEC.
Figure 3. MODIS satellite image of Matthew taken at 11:30 am EDT September 29, 2016. Image credit: NASA.
Short-term forecast for Matthew
The outlook for Matthew is fairly straightforward over the next couple of days. Late Wednesday, Matthew was moving due west at 17 mph, and a very gradual, well-predicted bend to a track just south of due west appears to be in progress. Along the way, conditions will favor at least some strengthening, as the atmosphere around Matthew moistens (relative humidity will rise from around 55-60% Wednesday to around 65% by Friday) and wind shear relaxes to around 10 knots by Saturday. There is fairly strong model agreement that Matthew will be positioned in the central Caribbean north of Colombia and south of Hispaniola by Saturday, perhaps as a Category 2 hurricane.
The outlook grows much more complex from this weekend onward. Models continue to agree that an upper low cut off from the jet stream over the eastern U.S. will extend into the Gulf of Mexico by the weekend, helping to urge Matthew northward. One big question is how far west Matthew will get before that sharp right-hand turn occurs. The longitude of the turn will help determine the westward extent of Matthew’s subsequent track, which in turn will shape whether Matthew threatens Cuba, Jamaica, and/or Hispaniola by early next week. The NOAA Gulfstream-IV aircraft that samples the environment around hurricanes is again in service after a multiweek outage, and data from the G-IV flights will be incorporated in model runs starting at 00Z Thursday, which should help nail down Matthew’s track.
Conditions may turn even more favorable for Matthew to intensify from around Saturday to Tuesday as it approaches the Greater Antilles. The official NHC outlook brings Matthew to the high end of Category 2 strength by Monday, when it is forecasted to be approaching eastern Cuba. There is only limited skill in predicting hurricane intensity five days out, and we cannot rule out the possibility that Matthew will intensify even more, or will fail to intensify very much. Rapid intensification is a distinct possibility, given the very large heat content in the northern Caribbean waters. Interests in the Greater Antilles, especially from eastern Cuba to the Dominican Republic, should pay especially close attention to Matthew’s progress. Matthew is a large storm and could lead to torrential rains and life-threatening floods and mudslides near its path in the Greater Antilles.
Figure 4. National Hurricane Center five-day outlook for Matthew as of 5 pm EDT Thursday, September 29, 2016.
Long-range forecast for Matthew
It appears increasingly likely that Matthew will move north from the Caribbean into The Bahamas and avoid the Gulf of Mexico, although residents along the Gulf Coast would be prudent to keep an eye on it. On Wednesday and Wednesday night, the European model included a minority of ensemble members that took Matthew into the Gulf later next week. In its 12Z Thursday run, the European ensemble became somewhat more unified around the idea that Matthew will move north into The Bahamas, then perhaps angle northwest from that point. The 12Z Thursday operational run of the UKMET model tracked along the same general lines as the Euro ensemble. Meanwhile, the GFS model and its ensemble members have been resolute for more than a day in taking Matthew through The Bahamas early next week on a steady northward track, with uncertainty growing as it approaches the Southeast and Mid-Atlantic coast.
Beyond The Bahamas, the GFS and European solutions leave open the possibility that Matthew could approach the U.S. East Coast anywhere from Florida to Maine, but the timing and location of that track remain very uncertain. Steering currents will hinge on the evolution of this weekend’s cut-off low in the eastern U.S. and on a new upper-level low that will be sweeping into the western U.S. It is far to soon to know exactly how these features will evolve. Next week’s upper trough could arrive in time to steer Matthew out to sea late next week, as suggested by the 12Z runs of the GFS and ECMWF operational model. However, any slowdown in that trough’s arrival, or any change in its configuration, could lead to a vastly different solution for Matthew—including a track angling inland. It is quite rare for such a trough to be perfectly predicted a week in advance.
The bottom line: Matthew will pose a significant threat to the Greater Antilles in the 3-to-5-day time frame, and a potential threat to the U.S. East Coast in the 6-to-10-day time frame. Future model runs will allow us to be more specific about the areas that will be most at risk and when that might be. As always, the five-day outlooks from the National Hurricane Center and the associated local bulletins are the place to turn for official guidance.
Jeff Masters will be back with our next update on Matthew by late Friday morning.
Figure 5. Track forecasts from (left) the five European model ensemble members that have performed best with Matthew thus far [gray lines], effective 12Z Thursday, September 29, 2016; and (right) the full 20-member GFS ensemble, effective 18Z Thursday.
30 foot significant wave heights (average of highest 1/3) at buoy north of center of Hurricane Matthew