Ana, Bill,--and Claudette?
After one of the slowest starts to hurricane season in the past twenty years, the hurricane season of 2009 has exploded with activity over the past 48 hours. This morning, Tropical Depression Four joined Ana and Bill in the Atlantic, and appears poised to become Tropical Storm Claudette later today. Indeed, this may already be Claudette, as morning's QuickSCAT pass showed top winds of 45 mph. NEXRAD radar animations out of Tallahassee, FL, show a small but well-organized tropical cyclone with plenty of heavy thunderstorm activity, and improving low-level spiral banding. Satellite loops show an area of intense thunderstorms with cold cloud tops expanding near the storm's center.
Figure 1. Current long-range radar out of Tallahassee, FL.
It's pretty amazing (and a little unnerving) how quickly this storm sprang up. TD 4 developed literally overnight, and has the potential to be a strong tropical storm by the time it makes landfall tonight along the Florida Peninsula. TD 4 reminds me of 2007's Hurricane Humberto, which became a hurricane just 24 hours after first appearing as a tropical depression. I don't think TD 4 has time to reach hurricane strength, since wind shear as diagnosed by the SHIPS model was moderate, 10 - 15 knots, but it does have time to strengthen into a 50 - 60 mph tropical storm before landfall. Given that the storm is so small, storm surge flooding should not exceed 3 -5 feet, and will not be the major hazard from TD 4; inland flooding from heavy rain of 3 - 6 inches is likely to be the main threat from the storm.
Tropical Storm Ana continues to struggle
Tropical Storm Ana continues to struggle. Dry air continues to plague the storm, thanks to the large area of Saharan air the storm is embedded in. Ana's heavy thunderstorms are limited to just one small spot near the center. Wind shear appears to have lessened some, though, since yesterday. Thunderstorms were not able to form at all near the center yesterday, since strong wind shear tends to blow a storm's heavy thunderstorms to one side of the storm, exposing the low-level center to view. With heavy thunderstorms building near the center this morning, shear appears to be less of a problem for the storm. Top winds seen by this morning's QuikSCAT pass were about 35 mph. The outer rain showers from Ana should appear on radar out of Martinique today.
Shear is low (5 - 10 knots), and is forecast to remain low for the next two days. SSTs are warm, 28°C, and will warm further over the next two days. However, there is so much dry air around Ana that significant strengthening appears unlikely. Nearly all of the models predict Ana will dissipate sometime in the next three days, though the HWRF and GFDL predict that this will happen because Ana will move over the rugged terrain of Hispaniola. Ana is likely not strong enough to survive an encounter with the big island that the Dominican Republic and Haiti share. At this time, it does not appear that Ana will be moist enough to cause a major flooding disaster on Hispaniola.
Figure 2. Water vapor image from this morning showing the large area of dry, Saharan air surrounding Ana, and lying to the northwest of Tropical Storm Bill. Image credit: NOAA/SSD
Tropical Storm Bill gathers strength
Tropical Storm Bill is gathering strength in the middle Atlantic Ocean, and appears poised to become a powerful Cape Verdes-type hurricane later this week. QuikSCAT data from this morning shows a large circulation with top winds of 35 - 40 mph. Water vapor imagery (Figure 2) shows that there is some dry air to the northwest of Bill, and this dry air is being drawn into Bill's center, slowing intensification. It will likely take another day before Bill can moisten the atmosphere enough to ward off the dry air, and allow more significant intensification.
Wind shear is low, 5 - 10 knots, and is forecast to be in the low to moderate range, 5 - 15 knots, for the next five days. Sea Surface Temperatures are about 27.5°C, and will remain in the 27.5 - 28°C range the next four days, then warm substantially as the storm nears the Lesser Antilles Islands. The combination of low wind shear and sufficiently warm SSTs should allow Bill to intensify steadily to hurricane strength by Wednesday.
The big news is that our most reliable computer model from last year--the ECMWF model--appears to have made the right call yesterday, forecasting that a major trough of low pressure would develop along the U.S. East Coast, turning Bill more to the north. All of the other models--with the notable exception of the UKMET model--have now jumped on the ECMWF bandwagon, forecasting that Bill will pass well north of the Lesser Antilles Islands. The UKMET has Bill hitting the islands, but is being discounted since it is an outlier. It currently appears that the trough approaching the U.S. East Coast will be strong enough to recurve Bill before it reaches the U.S., though it is too early to be confident of this. Several of the longer range models show Bill passing near Bermuda or Nova Scotia, Canada.
I'll have an update later today.
Jeff Masters
Reader Comments
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Link
Bill- 75mph winds
movement- WNW- 23mph
bill looks like a hurricane already!!! they gonna upgrade it the next advisary
ok
I think the GFS? Is showing its going to break through the trough though.. and it was an early model release, the rest may change soon.. the speed is just too great imo
IKE would never do that to you because you are best buds! Where did you hear this???
epic fail LOL
nop it will be has follow
at 5pm update
winds 65mph mb 994mbs
As I said earlier, probably the Freeport/Red Bay area in Walton county. Ike - got your slicker handy?
I would believe so!
Weatherstudent is not an expert.
We will find out!
Of all the so called mets on this site..StormW is the man..when he talks I listen
Veterans of storms have noticed that animals and bugs know when a storm is coming... ants begin to march and then disappear a few days b4 a storm hits, birds and squirls for days will frenzy feed and then disappear, even dogs, horses, etc, start to pace and get very nervous...animals can sense the pressure change days b4 humans can...and in my opinion, b4 computers
where do you get these gifs?
Hey may not be an expert, but I sure do enjoy his opinion.
Danny, Ericka, etc....?
I understand the limitations of radar data well, but a well defined storm will traditionally have completely closed off convection in the radar signature over the CoC. It may not be perfectly over the CoC, but it is closed. Example: Link
I think it is still there.
Not an epic fail, an epic win, for figuring out something!
Good down pour here!
By the sounds outside, it will be doing the same here soon...
Also, other culprits are Edouard, Hanna, Erica, Hilary, and a bunch more.
I also value StormW's opinion, and he is probably the closest one to an expert who comments on this blog.
Yes, I am joking. He is often in chat and last night he said Ana would hit Miami, Tampa, Mobile, New Orleans and then NYC.
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