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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Quoting 305st0rm:
what happened to ANA


Dry air...fast forward speed.
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74. IKE
Quoting futuremet:


System isn't going to hit the east-coast of the USA. Models are trending more and more to the east.
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Quoting hurricanelover236:

I never actually made a prediction about potential claudette. I only said what I knew Bill and Ana would do and once again, everyone was al worried about a florida hit and i said i can assure them that they are safe from both systems and now their assurance should be setting in.

They have not deviated, they are still threats you have not been proven right. Make this claim next week.
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does anyone know what time it could come ashore on the panhandle? I want to get my horses up and squared away by then.
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what happened to ANA
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twhcracker: My thinking as well. I'm sure those bands that are wrapping could easily have some 50mph gusts in them- and all it takes is a few of those with a few inches of rain to bring down trees. That's my worry- that we'll be getting some nasty bands.

I see how the high building in could move TD4 on a more westerly path but if it stays on it's present course then Tally is in line for some good rain and gusts.
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Quoting stillwaiting:
alot of people had doubt about the formation of td4 last night alot of nay-sayers,....and now this morning we do indeed have td4......how come none of the "models" picked up on the formation??????


Models are not always right and sometimes backyard storms are hard for them to pick up. I am impressed on how fast NHC classified TD#4. Goes to show you the NHC can make decisions without models developing systems in advance.
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Quoting twhcracker:


haha my local media has the usual holy roller bible thumpin tv show

I mean you closest local media outlet, NBC, CBS, ABC...
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That is a good point. Originally this thing was supposed to go in around Gulfport, MS.
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Thx Doc...
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Quoting Relix:
Local news are dimissing Ana and Bill already here in PR. Oh well... good luck to those in Claudette's path.

Yes, but I think they should be more cautious with Bill since there is lots of uncertainty on its track. Ana is almost a wave and to dry, is not much of an issue at this time;my two cents on this.
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Quoting P451:
Modis captures the large african wave that came off the coast yesterday... POOF?


why do you think POOF?
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Quoting gator23:
Quoting MandyFSU:
I'm curious about TD4's track. It looks like it's headed towards Apalachicola but many seem to think it'll go more towards Panama City? What is the thinking that would push it more westward vs the north-northwest track it's currently on now?

People were saying New Orleans yesterday. Just ignore some people and listen to youlocal media/NHC


haha my local media has the usual holy roller bible thumpin tv show
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Quoting sporteguy03:



Did uh you predict Claudette to hit FL???

I never actually made a prediction about potential claudette. I only said what I knew Bill and Ana would do and once again, everyone was al worried about a florida hit and i said i can assure them that they are safe from both systems and now their assurance should be setting in.
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weatherwiz: They have us under a flood watch here in Tally. I'm not worried about my house flooding, but those near the river may have problems (like with Fay last year) Mercifully, TD4 is moving a might faster than Fay was so that's good news. I'm excited for a rainy, breezy afternoon. That's the worst I hope for!
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homegirl - that mslp analysis is too coarse to capture TD4. for such a tiny storm you need a higher resoultion...and for that you need data. The quickscat hi res is about the only useful tool in the kit until ( and if) TD4's core goes right over a buoy.
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Quoting LACajunKid:
Amazing how quickly these things form. Live in Tallahassee and preparing for the arrival of Claudette.


i live north of pc, i think us and tallahassee could get the dreaded right quadrant if it comes ashore at destin or pensacola
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Quoting cajunkid:
td4 might stall for a little and go more west with the way that high is building.

Case in point.
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Well with the GOMEX the way it is I shouldn't be surprised with the extremely rapid formation of TD4/Claudette.
Member Since: August 10, 2009 Posts: 3 Comments: 672
Quoting MandyFSU:
I'm curious about TD4's track. It looks like it's headed towards Apalachicola but many seem to think it'll go more towards Panama City? What is the thinking that would push it more westward vs the north-northwest track it's currently on now?

People were saying New Orleans yesterday. Just ignore some people and listen to youlocal media/NHC
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td4 might stall for a little and go more west with the way that high is building.
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...Claudette looking to hit the Panhandle.
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Thanks Dr. Masters.
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so we should be good over here in okaloosa county correct
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alot of people had doubt about the formation of td4 last night alot of nay-sayers,....and now this morning we do indeed have td4......how come none of the "models" picked up on the formation??????
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Bill really looks like just a threat to Bermuda, but anyone along the East Coast should watch this storm very carefully. Any deviation in the models with the strength or placement of the trough will allow a closer Bill to track up the coast. Does anyone think that if Bill were to track up the East Coast he could be of the same strength as an Irene or Maria in 2005?
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Quoting MandyFSU:
Thanks weatherwiz- That is my gut feeling too. :)


Your welcome, Tallahassee will be on the wet side also and they probrally will get some heavy rain later as it gets closer.
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ANA looks sick
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Quoting WPBHurricane05:
I have to disagree with the Dr....I don't think wind shear was the problem with Ana yesterday...it was the dry air.


Dry air and its fast forward speed made the shear appear stronger than it really was.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
Quoting weatherwiz:


I been looking at the radar imagery and it looks like it is heading more north then west. Maybe because it is along the SW side of the high and the high pressure. I see it coming real close to Apalachicola.


Agree.
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Nice update. Thanks, homes.
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40. CJ5
Quoting jurakantaino:
There goes what's left of former Ana.............Link


You did see what she looked like yesterday morning, didn't you? I would say she is not gone yet, far from it.
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Bill looks well-organized, but you can tell there is dry air entrainment on the visible images. I still expect this to become a hurricane by tomorrow nonetheless.
Member Since: August 2, 2007 Posts: 19 Comments: 19234
thank you sporteguy
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thank you for the update dr masters.

however, im still surprised that you failed to mention anything at all about 91L (TD4, claudette) in your blog yesterday. patrap and a few others were actively talking about the possiblity of TC formation even before you released your blog yesterday.

and i do have to agree that the similarities with humberto are unnerving. i still think TD4 will strengthen into a weak TS with an outside chance of a very weak hurricane/strong TS.

and even though ana is looing rather bad this morning, i still dont think ana is done. she has come back from the grave on a few occasions already and even thought shes looking sickly now, once she enters the carribean i have a feeling she will restrengthen
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Is there more dry air in the atlantic during el nino's
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I have to disagree with the Dr....I don't think wind shear was the problem with Ana yesterday...it was the dry air.
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Tnaks Dr.Masters.

Bill going North would be good news.
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Local news are dimissing Ana and Bill already here in PR. Oh well... good luck to those in Claudette's path.
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Thanks weatherwiz- That is my gut feeling too. :)
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Quoting tharpgomex:
Sorry for this stupid question... but....what is the difference in tropical storm warning and tropical storm wind warning?


pretty much the same other then a wind warning is usually issued for inland counties as you won't get the storm surge there. Usually the NWS/NHC calls those Inland TS Warnings as opposed to the TS Warnings along the coast.
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Any chances of td4 slowing down. Really starting to gain convection.
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Thanks Dr. Masters.

Was wondering if TD4 will decrease SST's where it passes through

This buoy is at 28.5N and 84.5W - W. TAMPA 106NM West Northwest of Tampa, FL
Is this a normal variation?

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Quoting P451:
Dry air entrainment is pretty bad at the moment on Bill.







Which means it will head more west because it will stay weaker longer
Member Since: June 29, 2009 Posts: 13 Comments: 5300
All i can say is once again, i was rioght. Thats why people on here should take my advice. Everyone was getting hyped up about 2 potential florida hits and now like I said they are safe from both of these systems. I predicted Ana would stay weak and hit the islands. And i also predicted Bill would turn out to sea and im right on target. Thats why im scarcely wrong. Everyone was saying proof please when i made my predictions and well, now you have it. Bye Ana and bill.
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Quoting MandyFSU:
I'm curious about TD4's track. It looks like it's headed towards Apalachicola but many seem to think it'll go more towards Panama City? What is the thinking that would push it more westward vs the north-northwest track it's currently on now?


I been looking at the radar imagery and it looks like it is heading more north then west. Maybe because it is along the SW side of the high and the high pressure. I see it coming real close to Apalachicola.
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25. CJ5
Ana and Bill both had a bad night. Ana seems to like to dress up at night fall only to lose it in the am. She continues the walk of shame each morning. Dyr air is an issue with her but unlike last morning she has some convection around her coc. She continues to move W as does Bill. I think both of these are vigorous storms and it will take a lot of different dynamics to kill them off. Another watch and see day. I will say I do not believe the NW turn for Bill as earlier a modeled righ now. If Ana does follow the models she will cross the hottest waters anywhere in a few days.
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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.