Daweathablog

Charles E. Roop giving his own forecasts, weather discussions, photos and adventures for the Starkville, MS area, Florida, and beyond.

Friday, August 19, 2011

Watching Invest 97L

It's been a while, but it's a good time for a blog post since the fall semester is now here and the hurricane season is starting to ramp up.

I'll start with something that has been catching eyes in the meteorological community. For the last few days, guidance models have been developing a tropical cyclone (TC) to arrive fairly close to the southeastern U.S. coastline nearly a week from now. On Thursday, the NHC has designated this area of concern as Invest 97L.

NOAA
The vis-sat shows 97L as a decent wave with little shear in the environment. Shear analysis indicates values around 10 kts. Movement has been westerly at nearly 20 mph. Infrared satellite loops show more organization and colder cloudtops in the last few hours. There was some concern of what the Saharan Air Layer (SAL) surrounding 97L would do to it, but it seems that the SAL is not as intense as it was Thursday. It looks as if the wave is doing a good job avoiding dry air intrusions at the moment based on water vapor imagery.

So, what will happen? It's expected to approach the Lesser Antilies on Saturday where conditions could still be favorable for development. Shear is expected to be relatively low. The NHC is giving it a 40 percent chance of development for the next 48 hours. I'm confident that the chances will increase, at least through Saturday. Guidance models are in fair agreement of 97L moving toward the west-northwest and getting close to Puerto Rico and Hispaniola at the beginning of next week. What happens beyond that is iffy...

Path...
The system would eventually take a more northerly path. The GFS, at this moment, has the storm hitting the western side of Florida and striking the Big Bend next weekend. The Euro has the storm hitting the southeastern coast of Florida and moving north-northeast to northeast a day later than the GFS. It would depend on a) how strong the ridge to the east is and b) any troughs in the eastern U.S. to help "pick up" the storm. For example, the GFS seems to have the Bermuda High fairly strong and keep it more west than the Euro. Other models don't go this far out.

Strength...
If 97L / future TC moves over the islands (Hispaniola, Cuba), they can have an effect on further development of the system and even decrease its strength. The mountainous terrain can do some damage to a healthy TC. If the wave / TC doesn't cross the islands as much, it may not lose so much strength. It all goes back to the path of the storm, which is still highly uncertain.

Nutshell...
When I start to see consistant patterns in a guidance model (run-to-run) and the guidance models agreeing with each other, my eyes start to get wider. Still, I have a hard time trusting guidance models beyond three or four days. I'm not comfortable making calls this early in the game. My advice: People from the Carolinas to Brownsville, TX need to watch the tropics for the next week. Things might get interesting.

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