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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Bill and the US Uncertain


while the NHC continues to forecast a very close area of approach to the islands.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
New track more of a W or WNW'ly course initially, but then more of a NW component through 5 days. I would not be surprised, actually, if Ana moved south of the Caribbean islands.
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Wow didnt think Bill would be a fish storm being that far south.
Member Since: Posts: Comments:
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.

LOL, Tempted. He should I think.
Member Since: Posts: Comments:
2809. IKE
I'll never doubt you again ECMWF....on William,...er...Bill...

"THE ECMWF
WAS THE LEADER SHOWING A GRADUAL NORTHWARD TREND AHEAD OF A TROUGH
OVER THE EASTERN UNITED STATES A FEW RUNS AGO. NOW...THE REST OF
THE MODELS...WITH THE EXCEPTION OF THE UK MODEL...ARE FOLLOWING THE
ECMWF TUNE...AND ALL TURN BILL MORE THE WEST-NORTHWEST AND NORTHWEST
BY THE END OF THE FORECAST PERIOD."......


There is a chance Bill never crosses any land, except a threat for Bermuda.
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Quoting Tazmanian:
this is pathetic


what the


what the heck????



on bill??? the NHC is sleeping NO Way it will make that kind of turn i can tell you that right now if its going to make that kind of a turn it needs too do a vary hard right

Wont happen, promise.
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2806. Patrap
Member Since: July 3, 2005 Posts: 426 Comments: 128644
2805. nash28
Having said that, it is my honest opinion that if there is any U.S. landfall, it will be from the Carolinas NWD.
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Quoting Grothar:
The 11:00 PM advisories are out. Ana is trending further south and Bill appears to be going to make the turn eventually to the WNW then NW somewhere in the Bahamas. However, I know things may change as they always do.


Absolutely
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this is pathetic


what the


what the heck????



on bill??? the NHC is sleeping NO Way it will make that kind of turn i can tell you that right now if its going to make that kind of a turn it needs too do a vary hard right
Member Since: May 21, 2006 Posts: 5091 Comments: 115235
Hey guys...how are you doing tonight???
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Quoting srada:


that dosent look like "much" of a recurvature..
i know, lol
Quoting Relix:
Ana seems near dead again. I am tired of tracking so I am going to bed. I am expecting to wake up with Ana as a TD going south, Bill moving more W than expected a 91L still being 91L. We'll see... g'nite WU


Not so sure about that, but we shall see. Everyone writing off Ana yet again. Tropics can change fast......very fast. So do not call Ana dead yet.
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2799. Grothar
The 11:00 PM advisories are out. Ana is trending further south and Bill appears to be going to make the turn eventually to the WNW then NW somewhere in the Bahamas. However, I know things may change as they always do.
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Quoting jipmg:


well this is a first, looks like NOAHH is forecasting against the latest model runs =O

And building an ark.
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2797. sfla82
Yep..I as I expected Bill shifted further away from FL....And as for Ana...RIP soon, very soon! But again as I expected it is shifting further away from FL!
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Member Since: September 6, 2007 Posts: 0 Comments: 6594
2795. flsky
"Statement as of 10:10 PM EDT on August 15, 2009
... Fast moving line of strong showers and thunderstorms moving
across Lake... Orange... Seminole... and northern Brevard counties...
At 1005 PM EDT... National Weather Service Doppler radar indicated a
line of strong storms from Cape Canaveral to 9 miles south of
Clermont... moving north at 25 mph.
This line of strong showers and storms will move through
Lake... Orange... Seminole... Volusia counties with gusty winds of 45
to 55 mph. These winds can cause unsecured objects to blow
around... snap tree limbs or cause power outages. Occasional cloud to
ground lightning strikes can also be expected.
Torrential rainfall can be expected... causing temporary ponding on
some roads and minor flooding of poor drainage areas."


Getting closer. When a storm is approaching I listen for the thunder first (a common occurrence where I live), but sometimes what I hear is the basso profundo coming from someone's car speakers or the guy next door starting his Harley!
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In the discussion for Ana, it says that its moving too fast to intensify. Thats different from the usual dry air and shear.
Member Since: August 13, 2007 Posts: 10 Comments: 4158
Totally gut feel...but from what I see, none of these storms will have a major impact....:)
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2792. nash28
As for Bill, we still need to wait until he deepens enough and then look at the mid to upper level steering flow in accordance to the strength. Currently, Bill is being directed in the low level flow which will drive him on a 270-275 degree heading for the next few days. As he strengthens, he will begin to feel the mid to upper level influences and that is a few days away. There is a trough expected near the Great Lakes region in a few days. The stregth, position and orientation of that front will determine the ultimate fate of Bill and a U.S. landfall.
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2791. srada
Quoting canesrule1:


that dosent look like "much" of a recurvature..
Member Since: August 17, 2006 Posts: 1 Comments: 774
2790. IKE
Quoting lopaka001:


;=)
Agree
..waves at IKE!


waves back:)
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Bill's new projected path.
Member Since: August 9, 2009 Posts: 10 Comments: 5026
2788. Relix
Ana seems near dead again. I am tired of tracking so I am going to bed. I am expecting to wake up with Ana as a TD going south, Bill moving more W than expected a 91L still being 91L. We'll see... g'nite WU
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That is one heck of a pull north for Bill. Wont Happen that way sorry.
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Quoting mobilegirl81:
We might have Claudette monday morning.
very possible girl...at least the yard is done...battendown the hatches right?!!!lol
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2784. TayTay
Bill is large storm and it is a lot harder to predict its path and intensity. Right now it's almost impossible to forecast.
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2783. jipmg
Quoting canesrule1:


well this is a first, looks like NOAHH is forecasting against the latest model runs =O
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We might have Claudette monday morning.
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Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting IKE:


System looks pathetic.


;=)
Agree
..waves at IKE!
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I told you it wont be upgraded....it stays the same...
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2775. 996tt
Quoting truecajun:
looking at the water vapor loop, 91L seems to be weakening - i think - i'm still learning though, so correct me if i'm wrong


I hit that
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2774. RM706
NASH...long time, yeah I am the same... just monitoring mostly for fear of getting flamed.
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I think Bill Gates is conducting experiments on Ana.
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2772. jipmg
91L might blow up at night.. BILL is erupting, im expecting it to jump in wind speed tonight, ANA looking horrible.
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2771. Patrap
91L Rainbow Image

Member Since: July 3, 2005 Posts: 426 Comments: 128644
looking at the water vapor loop, 91L seems to be weakening - i think - i'm still learning though, so correct me if i'm wrong
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2768. JLPR
=O no change with Bill

...SUMMARY OF 1100 PM AST INFORMATION...
LOCATION...11.3N 36.6W
MAXIMUM SUSTAINED WINDS...40 MPH
PRESENT MOVEMENT...WEST OR 270 DEGREES AT 16 MPH
MINIMUM CENTRAL PRESSURE...1004 MB

im almost speechless xD
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2766. IKE
Ah-nah....discussion...

"...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."
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91 has a huge IR bloom coming off the coast now.
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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.