Ernesto moves inland, Tropical Depression 7 and African waves to watch - 8/9/12
Good afternoon everyone and welcome to my tropical weather update for Thursday, August 9th, 2012. We have two areas to talk about, but first I'd like to make a final mention of Hurricane Ernesto, which made landfall as a 85mph Hurricane in the Yucatan Tuesday night. Ernesto was more than likely a Category 2 hurricane at landfall, satellite showed continued intensification with a steady building eyewall and a well maintained CDO (Central Dense Overcast) several observations made by storm chasers revealed the pressure at landfall was around 975mb and winds where 90-100mph. This is consistent to what we saw as Ernesto moved into land and could very well be upgraded post-season as discussed in the NHC discussion. The only reason we didn't get a good handle on the intensity was due to a malfunction in the recon that caused the flight to be grounded until the next day.
Figure 1. A 975mb reading recorded by iCyclone chasers in Hurricane Ernesto.
Tropical Depression 7 forms in the Tropical Atlantic
The tropics have again lightened up with another system. Invest 92L became better organized the last day or so and managed to be declared a Tropical Depression just at 5pm. TD7 is again a rather tricky intensity and track forecast. The GFS model reveals that shear will be high as the system nears the islands and refuses to develop it into a system, this is also true with the ECMWF. The CMC and NOGAPS seem to develop this into a tropical cyclone, but are notoriously not as accurate as the GFS and ECMWF. Worth noting though that the ECMWF failed to develop Ernesto, Florence, and TD7 all in a row - this is why looking at models can only go so far and you really have to look at the situation at hand.
Figure 2. Satellite image of Tropical Depression 7.
Thanks to Ernesto, shear is generally high in the Western Caribbean however this will dissipate as Ernesto moves inland into Mexico. Should TD7 not open up into a wave due to the combination of high shear and very dry Saharan Air, it could have a shot at intensification once it reaches around Jamaica's longitude. This situation will probably be similar to Ernesto, as the trade winds in the Eastern Caribbean will act to cause TD7, or Gordon by that time, to become disorganized on the surface even though the satellite will probably be more impressive. Only gradual intensification is expected until the system reaches the Western Caribbean next week.
Figure 3. GFS 850-200mb shear forecast by 24 hours.
African wave to watch for development
Another area to watch for development is off the coast of Africa. The GFS has been consistently developing this into a tropical cyclone as it moves off the coast, with the exception of the 18z - 06z runs last night which did not develop the system, but was picked up again by the 12z. This system should it intensify quickly would probably be drawn more northward that Ernesto and TD7 are. We have several days to watch this system, the NHC currently gives this a 20% chance of developing in the next 48 hours and I would place my odds at 30%, due to an abundance of dry air.
Figure 4. Satellite image of the African Wave.
I will admit, I am impressed with the pace of activity we have been having in August. We are facing the possibility of having Tropical Storm Gordon tomorrow, well ahead of schedule. Indeed, the 2009 Atlantic Hurricane season didn't get 'Grace' until October, and 2006 didn't get its Gordon until early September. This has caused Colorado State University and Tropical Storm Risk to raise their August predictions to both 14 named. The August predictions are generally more accurate of the predictions and are the last.