Ana, Bill,--and Claudette?

By: Dr. Jeff Masters , 1:52 PM GMT on August 16, 2009

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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

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A very tight curve band, should serve the focal point of an eye featre

we also officially have Caludette

Member Since: July 24, 2005 Posts: 407 Comments: 19076
TWC say TD 4 is now Claudette.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
we have a Tropical Storm Now
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does anyone think theres a chance of Td4 center reforming? It's a huge area and the COC is moving completely out of the clouds, which seem to be building southward!



Member Since: July 29, 2006 Posts: 28 Comments: 1791
Quoting IpswichWeatherCenter:


Thats a closed low.
not really, and its waaaaay to broad.
Quoting IpswichWeatherCenter:


Thats a closed low.


Last night Dr. Lyon
Quoting jpsb:
I am pretty sure he said yesterday (maybe friday) that nothing would come of the wave in the Fla keys. lol, that is when I decided I needed to watch that wave. Dr Lions really blew that call.


You're correct
Yesterday evening, Dr. Lyon's was saying that the wave wouldn't develop.
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456 do you thin TD4 is moving NNW or NW? Im looking at the outer bands in the far NW of the system?
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Quoting canesrule1:
WTF is up with the Windsat, no closed low:



Thats a closed low.
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Claudette making a left turn.
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IF pressure is building over panhandle TD4 will be interesting to watch. I remember in the 80's a storm that switched directions twice and moved back and forth along the gulf coast. Not saying that will happen but it can.
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Allstar17

Glad you see the same thing as I. These graphics do play tricks on one's eyes sometimes.
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Patrap, Your last radar image looks like WNW which is really not good. Mobilegirl, you may be right.
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TD 04's current recon max wind: From 105° at 17 knots
(From the ESE at ~ 19.5 mph)

Current Lowest pressure: 1013.2 mb
(~ 29.92 inHg)
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WTF is up with the Windsat, no closed low:

Quoting Grothar:
Thank you Drak. Then it is not my imagination. It would appear that low pressure to the North of Ana is moving in tandem (is that a correct word?) Could it affect the current NHC track?


Possibly
Member Since: October 28, 2006 Posts: 57 Comments: 30490
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Note at day 5, Bill is at 25 N...the same latitude of the extreme southern tip of Florida.

No one is off the hook in the Lesser Antilles, Bahamas, and the East Coast till Bill moves north of your latitude.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Thank you Drak. Then it is not my imagination. It would appear that low pressure to the North of Ana is moving in tandem (is that a correct word?) Could it affect the current NHC track?
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554. JRRP
Quoting DestinJeff:
Man, Dr Lyons looks like Mr Burns

LOL...
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Isn't there a ridge of high pressure to TD4's north? Wouldn't the steering be more of a westward pattern because of the ridge influencing it?
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Quoting extreme236:


I dont think the ADT position for the center is correct.
me either
551. jpsb
Quoting DestinJeff:
Man, Dr Lyons looks like Mr Burns
I am pretty sure he said yesterday (maybe friday) that nothing would come of the wave in the Fla keys. lol, that is when I decided I needed to watch that wave. Dr Lions really blew that call.
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Quoting Drakoen:


Ana may be feeling a tug from the synoptic features to it's north. There is a big upper level low near the Bahamas. Ana could head more towards the northern islands



I see Bill heading towards the WNW


I still do see a circulation with Ana. Also, TD 4 should be Claudette soon enough. I also see a more WNW'ly course over the last hour or so.
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Look from what I see with TD4 or Claudette, If the storm goes on a west NW movement then it could be just like hurricane Cindy back in 05... Cindy was to be a Tropical Storm at land fall but was changed to a Hurricane after the fact..... This could happen.....

Just my thinking....

Taco :0)
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Link

Getting breezy south of Apalachicola
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The wishcasters that keep insisting that Bill wasn't a fish have gotten a little quite now!!! LOL! So again RIP to Ana and Bye bye Bill! Florida is officially in the clear!
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Quoting sfla82:
The wishcasters that keep insisting that Bill wasn't a fish have gotten a little quite now!!! LOL! So again RIP to Ana and Bye bye Bill! Florida is officially in the clear!


And bye-bye to you! How do you know what will happen?
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Quoting canesrule1:
WOW, bill has a weakening flag, ANA has a rapid dissipating flag, and 04L will probably become claudette at 12:30 or 1


I dont think the ADT position for the center is correct.
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Tropical Depression Four formed in the eastern Gulf of Mexico on August 16. The disturbance developed rapidly and formation was not expected until just a few hours before its declaration as a tropical depression. As recently as 9 hours before the storm's formation, the NHC gave the system a less than 30% chance of developing in the next 48 hours.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting WPBHurricane05:


Those aren't my thoughts. I'm very vigilant of Bill.


So am I. I think some people are jumping the gun a bit. Nothing is a certainty
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recon is still not close to 04L's center yet
Member Since: October 28, 2006 Posts: 57 Comments: 30490
Quoting AllStar17:


To the south and west, right. That may not be entirely good. If the system hangs on and gets into the extreme TCHP of the Caribbean this could blow up rapidly if it hangs on. I do not see this going over any of the islands, I see it going south of the islands.


I second that
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The wishcasters that keep insisting that Bill wasn't a fish have gotten a little quite now!!! LOL! So again RIP to Ana and Bye bye Bill! Florida is officially in the clear!
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Quoting FLGatorCaneNut:
SO.....thoughts now are that Bill will be a Fish Storm


Those aren't my thoughts. I'm very vigilant of Bill.
Member Since: July 31, 2006 Posts: 56 Comments: 8112
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Grothar:

Hi Drak, The last few frames on the NOAA site shows a consistant flare-up of convection further to the North of where Ana's position was recorded. Also, Bill seems to be taking a slight turn South. I know amateurs always see a lot that isn't there, however, I would like your opinion.


Ana may be feeling a tug from the synoptic features to it's north. There is a big upper level low near the Bahamas. Ana could head more towards the northern islands



I see Bill heading towards the WNW
Member Since: October 28, 2006 Posts: 57 Comments: 30490
wow, just had a "mahache" (water tornedo) blow through the island...first "weather" we have had since February.
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Quoting Barbados:


Allstar17. What do you mean about going south of the islands. The Caribbean islands stop at Trinidad whish is further south than Barbados.


South of Puerto Rico, Hispaniola, Cuba, the Virgin Islands, and the Northernmost Leeward Islands
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Quoting atmoaggie:
CHIPS has fallen in step with the others further (except for one ensemble member).


1. Would it not be interesting if the little bump in intensity at 36 hours can to fruition?
2. And just what would be the cause of that? Dry air entrainment?


Ocean Heat Content change?
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Quoting HurricaneJoe:


I'll give you props, you called the system in the Gulf correctly. Now, what do your 'sources' think it's going to do?
His source may have been the several folks who were watching and reporting on the system for the last few days. A recap WITH CAPS! LOL
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Quoting Ossqss:


Thanks, the last run had a vanishing Ana. In my novice eyes :)

Ana and td-4 are both, really, too small for GFS resolution. Ana might vanish, but I don't think GFS is really capable of forecasting that outside of the accidental "lost" system because it fell between grids points at some point in time.
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What a change from 3 days ago where they had it all over Florida
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525. IKE
TD4 looks impressive on satellite.

I'll be surprised if it's not a TS.

Pressures high, not sure why?
Member Since: June 9, 2005 Posts: 23 Comments: 37858

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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

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