Beware the model wars: It’s a long way to any threat

Good morning.

It’s getting busy in the tropics, but there are many misconceptions. If you only listened to some amateur voices that have no meteorological background, you would think a major hurricane might be threatening the east coast soon based on a few model runs. Make no mistake, it’s getting active out there, but any threats (if they do evolve) are many days away. There are three systems out there, one of which is dying (for now at least), one of which is slowly inching up and one of which is on the verge of becoming a cyclone.

Current satellite image of the broader Atlantic (image from NHC/NCDC) annotated showing current systems as of 11 am EDT August 22, 2016.

Current satellite image of the broader Atlantic (image from NHC/NCDC) annotated showing current systems as of 11 am EDT August 22, 2016 and most likely direction of travel in the next 3 days or so.

Tropical Depression Fiona

Strong shear continues unabated in the central Atlantic and dry air is also a problem. Even though warmer seas have allowed Fiona to maintain some deep convection and persist as a tropical cyclone, it has weakened to a tropical depression with estimated 35 mph sustained winds and is barely hanging on right now. It may lose its convection and become a remnant low at any time and may fully dissipate in the next couple days. However, if it survives the next 36 hours or so, an opportunity for redevelopment exists starting early Wednesday, as some models suggest.

Disturbance/Invest 99L

This weekend, the talk was on this low that appeared to be heading for development. However, the same conditions inhibiting Fiona have slowed this system down too. The majority of models (but not all) suggest it will develop late this week near or north of the Leeward Islands, Puerto Rico and Hispaniola. The NHC gives it a 20% chance of development by early Wednesday (likely generous) and 50% chance by week’s end (likely conservative). I believe this will become Tropical Depression Eight (see below) by late this week, and perhaps Tropical Storm Hermine as we get towards the weekend.

Disturbance/Invest 90L

A much larger and better organized low has already emerged off of Africa and is currently located near the Cabo Verde islands. The NHC says development into a tropical cyclone is imminent, and I agree it should become Tropical Depression Seven soon (if it isn’t a tropical cyclone already) and Tropical Storm Gaston within the next day or so. Most models develop this system into a large and powerful hurricane in the central Atlantic, so it is not unreasonable that we could even get the first major hurricane of the season from this. That said, it is extremely far from any land.

ECMWF: Ridge holds firm
ECMWF model run (00Z August 22) for next Monday evening (8 days out) showing surface pressures of 500mb heights. Fiona is long gone, 90L becomes powerful Hurricane Gaston as it recurves, while Tropical Storm Hermine sits off the Florida coast.

ECMWF model run (00Z August 22) for next Monday evening (8 days out) showing surface pressures of 500mb heights. Fiona is long gone, 90L becomes powerful Hurricane Gaston as it recurves, while 99L becomes Tropical Storm Hermine and sits off the Florida coast.

Simply put, any threats are at least 7 to 10 days away, if they even try to come our way. Fiona is the closest system, but it will have a hard time surviving the next couple days. The strong ridging in the upper atmosphere over the Continental US and northern Atlantic will likely slow these storms down and make them susceptible to erratic movements. It appears 99L (if it develops) will end up trapped in the Bahamas or near Florida, while 90L will end up trapped not too far from Bermuda. That is what the ECMWF suggests.

GFS: Delayed development of 99L
GFS full-resolution image from the 06Z August 22, 2016 run, also for next Monday evening. The intense hurricane on the eastern edge of the map is 90L now, while 99L and Fiona are weak lows.

GFS full-resolution image from the 06Z August 22, 2016 run, also for next Monday evening. The intense hurricane on the eastern edge of the map is 90L now, while 99L and Fiona are weak lows.

Meanwhile, the other reliable model, the GFS, keeps a weak Fiona vortex alive through the week, while 99L does not develop until it reaches the Florida Straits or the eastern Gulf (eventually hitting the Florida Panhandle at near the hurricane threshold). 90L stays safely away from land, never making it west of 55W longitude, but becomes an extremely strong Category 4 or 5 hurricane in the process. After that, it may either escape to sea or move westward for a while. The intensity forecast does seems overblown for its location. Either way, the threat for the east coast as of right now is very low.

GFS ensemble mean positions (06Z August 22 run) for next Monday night. The ensembles are in good agreement that 99L will be a weak low near Florida, while 90L will be a powerful hurricane east of Bermuda.

GFS ensemble mean positions (06Z August 22 run) for next Monday night. The ensembles are in good agreement that 99L will be a weak low near Florida, while 90L will be a powerful hurricane east of Bermuda.

The GFS ensemble trends also agree with our analysis. They are almost unanimous on 99L remaining weak through the Bahamas and Fiona largely dissipating. In addition, they are also in good agreement that 90L will develop into a powerful hurricane in the central Atlantic. Either way, it looks like the east coast should remain clear for the next little while as the ridge acts to protect us from any significant tropical activity. Beyond 8 days the models can go wild and do weird things, so that is too far away to really make any additional forecasts.

Conclusion

Hurricane season is starting to enter its peak and we may add two more storms, including one more (major?) hurricane, by week’s end. The east coast is expected to be well protected by a strong ridge of high pressure aloft over the next week, which will likely keep these systems well away from the coast for the foreseeable future. They will still be out there and the tropics are erratic so we still need to keep an eye out. One thing for sure, though, is that we should primarily listen to good reputable meteorologists for an analysis since they have the best information available. Let’s avoid wishcasting or hype and focus on real information.

Forecaster Craig Ceecee – @Ceecee_Wx

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