Ana and TD 3 take aim at the Lesser Antilles

By: Dr. Jeff Masters , 4:17 PM GMT on August 15, 2009

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Tropical Storm Ana was born this morning, when the remnants of Tropical Depression Two made a comeback and organized into the first tropical storm of the 2009 Atlantic hurricane season. Ana is the latest first named storm of the season since Hurricane Andrew got its name on August 17, 1992. The two storms have some similarities, as Andrew formed in the same part of the ocean, and also struggled in its early days with high wind shear and dry air. Let's hope the similarities end there.

Ana is struggling this afternoon. After an modest burst of heavy thunderstorm activity prompted NHC to upgrade Ana to a tropical storm early this morning, Ana has run into strong upper-level winds from the west that are creating high wind shear. This shear was not forecast, and it is not clear how long it will last. The shear has acted to drive dry air into the core of Ana, destroying almost all of Ana's heavy thunderstorms. The low-level center of the storm is now exposed to view, something that often foreshadows the death of a storm. It is possible the shear will destroy Ana, and several models (the GFS and ECMWF) forecast this may be the case. However, the shear forecast calls for shear to drop into the low range, 5 - 10 knots, tonight through Tuesday. If the shear does drop as forecast, Ana should be able to moisten the atmosphere around it sufficiently to protest itself from the dry Saharan air that surrounds it (Figure 1). SSTs are 27°C today, and will increase to 28°C by Sunday. By the time Ana moves into the Bahamas, total ocean heat content rises steeply (Figure 2), and rapid intensification of Ana is possible, if the shear and dry air haven't disrupted the storm. The intensity forecast models, for the most part, predict a steady intensification of Ana to the threshold of hurricane strength five days from now. The HWRF model is on the strong side, predicting a Category 2 hurricane. The GFDL predicts a weak tropical storm five days from now, but that is because the model has Ana passing over the rugged terrain of Hispaniola, something the other models do not predict. In summary, the intensity forecast for Ana has higher than usual uncertainty, and I give equal chances that the storm will be a hurricane--or non-existent--four days from now.


Figure 1. Water vapor image from this morning showing the large area of dry, Saharan air surrounding Ana, and lying to the north of Tropical Depression Three. Image credit: NOAA/SSD

Tropical Depression Three forms, could be Bill later today
QuikSCAT data from this morning and satellite loops revealed that the tropical wave (90L) in the middle Atlantic has finally developed a well developed surface circulation and can be classified as Tropical Depression Three. Recent satellite imagery suggests that TD 3 may already be Tropical Storm Bill. Water vapor imagery (Figure 1) shows that TD 3's center consolidated a few hundred miles south of the dry air of the Saharan Air Layer (SAL). Thus, the storm should not be affected by dry air and dust as much as Ana has been. Ana may also act to moisten the atmosphere in front of TD 3, helping protect the storm from the SAL as it edges farther north over the the three days.



Figure 2. Heat content of the ocean, in kJ per square cm. Oceanic heat content steadily increases for Ana and TD 3 as they approach the Lesser Antilles Islands. Oceanic heat content levels of 90 kJ per square cm are frequently associated with rapid intensification of hurricanes. Image credit: University of Miami.

Wind shear is moderate, 15 knots, but is forecast to fall to 10 - 15 knots on days 2 - 5. Sea Surface Temperatures are about 27.5°C, and will remain in the 27.5 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow TD 3 to intensify steadily, and I expect the storm will be at hurricane strength by Wednesday, when it will be near the northern Lesser Antilles Islands. Most of our reliable intensity models strengthen TD 3 into a hurricane by Wednesday. Oceanic heat content (Figure 2) increases sharply just before the islands, so TD 3 could be intensifying rapidly as it moves through or just north of the Lesser Antilles on Thursday. TD 3 consolidated farther south than expected, so the track models calling for a more northerly path were probably incorrect. In particular, the ECMWF model, which had TD 3 turning sharply northwestward and missing the Lesser Antilles Islands, was probably much too far to the north in this morning's 00Z run. TD 3 will probably pass very close to the northern Lesser Antilles islands on Wednesday and Thursday.

I'll have an update Sunday.

Jeff Masters

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Quoting CatastrophicDL:

Yep, you're keeping the halo shiny!


I am a changed person.. nothing but S&I now :)
Member Since: October 1, 2007 Posts: 81 Comments: 26511
Bill is the one to watch: Link
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2962. hartfa
Educated guesses regarding 91L? My three teens are working with Rebuild NOLA this week and 91L is definitely piquing my interest!
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img src="" alt="" />
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2958. jpsb
Quoting Orcasystems:


I have been coming here for years..and at times I sense stupidity.. but I don't say it :)
Lol, I'll risk it, off topic but why do I have to hit the "show" button to see some posters posts? thanks.
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2956. scCane
I think bill is either going to be a fish or a north carolina storm simply by where the models take it, north of puerto rico.

Just a estimate right now going simply by history.
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Quoting Orcasystems:


I have been coming here for years..and at times I sense stupidity.. but I don't say it :)

Yep, you're keeping the halo shiny!
Member Since: September 3, 2007 Posts: 3 Comments: 1519
Ana continues to underwhelm us. Bill is the one to watch IMO
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2953. GatorWX
91L is beginning to look better amd better. going off radar, looks like convection is over the center and banding is forming. Wouldn't completely wrote this off. May have slight potential at attaining depression strength.
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Quoting DM21Altestic:
the Bermuda high is too strong to allow Bill to be a fish storm.

I agree, nothing is getting out.
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2951. nash28
Altestic-

You need to check the AB high in about four days once we have a core system that is feeling the mid to upper levels of the atmosphere and then check the steering flow in said levels.
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Quoting WeatherStudent:



And with good reason too, why would he?


alllllll right. sassy pants.
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Quoting DM21Altestic:

Nothing more than a strong TS possiblity.


I hope so. But don't turn your back on it. From a Humberto "survivor" lol.
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Quoting DM21Altestic:
the Bermuda high is too strong to allow Bill to be a fish storm.


agreed
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Hi Wunderweatherbloggers. Avila doesn't have much respect for Ana:
Tropical Storm ANA Forecast Discussion
WTNT42 KNHC 160247
TCDAT2
TROPICAL STORM ANA DISCUSSION NUMBER 16
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL022009
1100 PM AST SAT AUG 15 2009

THE CONVECTION NEAR THE CENTER OF ANA HAS BEEN PULSATING AND AFTER AN INCREASE FOR A FEW HOURS...THE LOW LEVEL CENTER HAS BECOME EXPOSED AGAIN. THIS MEANS ANNA IS NOT STRENGTHENING AND THE INITIAL INTENSITY IS KEPT AT 35 KNOTS. A NOAA JET FLEW AGAIN TONIGHT AND ONE OF THE DROPS NEAR THE CENTER MEASURED A SURFACE PRESSURE OF 1004 MB WHICH WAS USED FOR THIS ADVISORY. THE SHEAR IS NOT VERY STRONG AS DIAGNOSED BY THE SHIPS MODELS BUT THE LOW-LEVEL CENTER OF ANA IS SIMPLY MOVING TOO FAST. THIS RAPID MOTION IS PROBABLY NOT TOO CONDUCIVE FOR INTENSIFICATION. IN FACT...THE ONLY DYNAMICAL MODELS THAT KEEP ANA ARE THE UK AND THE NOGAPS. THE REST OF THEM WEAKEN ANA TO A TROPICAL WAVE. I AM TEMPTED TO SHOW WEAKENING BUT FOR NOW...I AM GOING TO FOLLOW THE PREVIOUS FORECAST AND SHIPS MODEL GUIDANCE. THE OFFICIAL FORECAST SHOWS SLOW STRENGTHENING THROUGH 48 HOURS FOLLOWED BY WEAKENING AS THE CYCLONE INTERACTS WITH HISPANIOLA AND CUBA.

THE INITIAL MOTION IS 270/15. ANA IS EMBEDDED WITHIN STRONG AND PERSISTENT TRADE WINDS AND ONLY A SMALL TURN TO THE WEST-NORTHWEST WITH AN INCREASE IN FORWARD SPEED IS ANTICIPATED. THE OFFICIAL FORECAST IS A LITTLE BIT SLOWER THAN MOST OF THE GUIDANCE BUT IS WELL INSIDE THE ENVELOPE THROUGH 48 HOURS. THEREAFTER...SOME MODELS KEEP A WEAKER ANA SOUTH OF CUBA AND OTHERS BRING THE CYCLONE OVER
CUBA AND INTO THE GULF OF MEXICO. THE OFFICIAL TRACK FORECAST IS VERY SIMILAR TO THE PREVIOUS ONE AND FOLLOWS THE NORTHERNMOST GROUP
OF MODELS.
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2945. JLPR
Bill is looking impressive and I just dont see it as a Fish
Right now I believe the UKMET track
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Quoting fire831rescue:
Anyone have any info on 91L? I've searched all over and can't find any info. Just curious as to what it's doing...


91L is deepening. Radar shows nice LLC and even possible banding features. Not much time for strengthening, obviously...but I'm calling TD04 by 5am.
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2943. Drakoen
At 270 degrees, Bill is moving due west. The slightly south of due west motion has come to a halt.
Member Since: October 28, 2006 Posts: 57 Comments: 30562
Quoting Maighstir:


Great post!


HI! Haven't heard from you in a while. How are you?
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All good luck, Florida.

Watching the east coast closely.

Hey maybe we're going to catch up with the Pacific, yet.



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2940. 2ifbyC
Nothing on the local news, WFLA Tampa, about the circulation just of the coast. I'm in Bradenton and expecting a bunch of rain by daylight tomorrow!
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Quoting fire831rescue:
Anyone have any info on 91L? I've searched all over and can't find any info. Just curious as to what it's doing...


Hey Fire! Glad to see you. I am looking for the same. That one has my interest right now.
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Quoting winter123:



ALL CAPS AND BOLD MAKES YOUR SMARTER


No that was not my intention, just had problems with the internet and the post appeared twice. Regarding the bold and caps i did it so that the text could appear without being overwhelmed by the image. Sorry if it bothered you, it's been a long time since my last post.

:D
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Ok for everyone thinking Bill looks Strong (Like Hurricane) is wrong. Yes he's better Organized than Ana but what's really happening is your looking at Bill and you see a "bigger" system compard to Ana. You have to look at more than just its size.
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caution: model shifts
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Quoting nash28:
Taz- You know better than to listen to trolls.

The UKMET has been so far out to lunch in since 2005 it's laughable.

The UKMET hasn't even initialized properly with either storm
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Just remember, Ike was supposed to also turn out to sea.

Its too far out to know.
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Quoting fire831rescue:
Anyone have any info on 91L? I've searched all over and can't find any info. Just curious as to what it's doing...


http://www.ssd.noaa.gov/PS/TROP/float3.html
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I see we have a new invest 91L.
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CHIPS reigned it in a bit. Might turn into a useful application of flops, yet.


http://wind.mit.edu/~emanuel/storm.html
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Anyone have any info on 91L? I've searched all over and can't find any info. Just curious as to what it's doing...
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2925. nash28
Taz- You know better than to listen to trolls.

The UKMET has been so far out to lunch in since 2005 it's laughable.
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Quoting mtyweatherfan90:
Bill still looks impressive, it should be at least a strong tropical storm by now.



CONVECTION IS GROWING RAPIDLY AND IS SURROUNDING THE CENTER, KEEPING A W-WSW MOTION.



ALL CAPS AND BOLD MAKES YOUR SMARTER
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Quoting nash28:
Once again, for the cheap seats ladies and gentlemen, the models right now past five days are crap. Crap. It is a TS. A low level flow TS. Anyone with eyes and a steering flow map can see what the steering flow will be like for the next few days. Anyone guessing after that, INCLUDING the models is just guessing. It's all about the AB high, the AB high bridging with the NE ridge and the trough.


Great post!
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My weather lady didn't mention 91L either..instead said that the moisture is dying down, that while we were in Ana's cone that it really should NOT affect us...not to look at the center of the cone, rather the 200 miles to either direction, and that Bill will go out to see. Completely downplayed. I am in Cape Coral...I was a little surprised seeing as how just the other day they were all hyped up calling td2 Ana two days before she was actually named!
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2919. jipmg
Quoting AussieStorm:

Some models say he will.


notice how they are moving it WNW at this point, and its still moving south of due west
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Bill still looks impressive, it should be at least a strong tropical storm by now.



CONVECTION IS GROWING RAPIDLY AND IS SURROUNDING THE CENTER, KEEPING A W-WSW MOTION.
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bounced in for just a few...the storms aren't even hurricanes yet and ppl are already at each others throats...let's face the facts...everyone from the islands to the gulf and the entire east coast need to watch these storms...prime example...HUGO! According to the computers Charleston was NOT supposed to get hit...by the time they realized it was headed here...it was pretty much too late to do anything...most were stuck, no supplies, etc...I don't trust the models more than 24-48 hours out...storms jog all the time...besides, they are way too far out to predict anything at this point. (stepping off my soap box now)
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Quoting WeatherStudent:
:( Oh well, I guess it's time for moi to begin looking off the African coastline yet again tonight for the next tropical wave that might have TC potential.


get some help
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Quoting Skyepony:
~


YES!
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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.