Atlantic tropical disturbance 91L poses little threat

By: Dr. Jeff Masters , 2:15 PM GMT on April 21, 2011

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A tropical disturbance (91L) near 24N, 63W, midway between the Virgin Islands and Bermuda, is moving north-northwest at about 8 mph. The system's heavy thunderstorm activity has increased since yesterday, but 91L has an elongated and poorly-organized circulation, thanks to a hefty 80 knots of wind shear. The storm is over waters of 25°C, and these waters will cool to 24°C by Friday as the storm continues to the north-northwest. Before 91L reaches Bermuda, steering currents will reverse and force 91L to the south-southwest on Saturday, into a region of higher wind shear. The latest SHIPS model forecast predicts wind shear will drop to 50 knots over 91L by Friday, then increase again to 70 knots by Sunday. The high shear and relatively cool water temperatures will make it difficult for 91L to organize into a subtropical depression. I give 91L a 10% of becoming a subtropical depression. Climatology argues against 91L becoming the first named storm of the year; there has only been once named April storm in the Atlantic since 1851, Tropical Storm Ana of 2003. The formation of a tropical disturbance at this location this time of year is unusual, but is not necessarily a harbinger of a active season ahead.


Figure 1. Morning satellite image of the Atlantic tropical disturbance 91L.

Jeff Masters

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Quoting Levi32:
The old center is becoming wrapped up in a larger circulation now. Notice how the main swirl is moving northward on the east side of a larger spin.

RGB Loop


Yeh, I think the centre has moved to the north-west. Probably explains why we lost the westerlies earlier today.
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Quoting Levi32:
The old center is becoming wrapped up in a larger circulation now. Notice how the main swirl is moving northward on the east side of a larger spin.

RGB Loop


I see what you mean...looks like the old circulation is more mid-level.
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The old center is becoming wrapped up in a larger circulation now. Notice how the main swirl is moving northward on the east side of a larger spin.

RGB Loop
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting Stormchaser2007:
Structure continues to improve. 


Looks pretty good on the loop. You can tell the circulation is still elongated north to south, but there are west winds at least at the mid levels.
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Looks like Invest 91 could maintain intensity and undergo complex subtropical strengthening contrary to SHIPS as it tracks over the Gulf stream carrying warm water from the western Caribbean Sea. It could then be absorbed into a developing North American storm.
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Quoting RastaSteve:


I swear I saw a couple of nights ago a lady say that on that Channel no lie. This was no mix up. I think she's on with Paul Goodman. I was shocked that she said that infact I looked over to my wife and said I can't believe I just heard that.


Confirmation. I heard them say it too...
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Structure continues to improve. 
Member Since: June 9, 2007 Posts: 4 Comments: 15889
Quoting jeffs713:

Understand you there. Its amazing how much we rely on the internet. You don't realize how important it has become to our daily lives until it isn't there. (Kinda like watching people drop absurd amounts of money checking e-mail and facebook while on a 5-day cruise)
LOL the "net" is really addictive. I discovered, when I was on-line at home, that I really, really, really, like games. Couldn't get off until late. Then dragged the next day. So I think it is in my best interest to NOT have internet at home. At least I am allowed to surf while at work as long as I get my work done.
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Quoting MississippiWx:


In your defense, I was watching TWC during that tornado outbreak and it was Heather Tesch that was saying that stupid crap. She told someone she was interviewing that, "Isn't it true that staying in your car is actually safer than lying flat in a ditch? I've seen a lot of new research lately that says you should just stay put in your car."

She is an idiot, as well as most everyone on that channel.

Not to mention, its really safe being surrounded by glass during an event that has flying objects moving at 100+mph.
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Quoting kwgirl:
I know, but I am not on-line at home. So back to the old fashioned watching TV, looking at the radar sweeps and determining for myself what is going on. It is going to be rough on me this hurricane season. I used to put up the KW radar on my computer sitting snug in my home watching storms approach. Now, I am going to be "tucking tail" and running like crazy for every little Cat 1 on. Pathetic. But that is where I am at the moment so I have to deal.

Understand you there. Its amazing how much we rely on the internet. You don't realize how important it has become to our daily lives until it isn't there. (Kinda like watching people drop absurd amounts of money checking e-mail and facebook while on a 5-day cruise)
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Quoting RastaSteve:


Nothing else on TV! Pretty lame shows lately on TV and the Magic weren't playing that day. Last resort.


In your defense, I was watching TWC during that tornado outbreak and it was Heather Tesch that was saying that stupid crap. She told someone she was interviewing that, "Isn't it true that staying in your car is actually safer than lying flat in a ditch? I've seen a lot of new research lately that says you should just stay put in your car."

She is an idiot, as well as most everyone on that channel.
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Quoting jeffs713:

Eh, I avoid TV for weather in general. MUCH more raw information to be had on the 'net.
I know, but I am not on-line at home. So back to the old fashioned watching TV, looking at the radar sweeps and determining for myself what is going on. It is going to be rough on me this hurricane season. I used to put up the KW radar on my computer sitting snug in my home watching storms approach. Now, I am going to be "tucking tail" and running like crazy for every little Cat 1 on. Pathetic. But that is where I am at the moment so I have to deal.
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Quoting kwgirl:
Sometimes you have to watch it just to catch up on the disastrous weather. They are good at showing that. Last week when those tornadoes were spawning, it was the only channel with any information.

Eh, I avoid TV for weather in general. MUCH more raw information to be had on the 'net.
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167. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 5807
Quoting RastaSteve:


I don't know about drought busting but yes some will fall from this here but we may get more from the afternoon thunderstorms as a result of increased moisture this weekend thru next week. Infact the NWS in Tampa is saying no rain this weekend when the models say otherwise. Shocking! GFS infact is painting a fairly active day Sunday as a trough slides across the guld and meet increasing moisture from the SE.


Yeah forecasters have been very conservative lately in Central Florida, just like they were with that severe weather event a few weeks back. Literally just 3 days before that hit they had us with a 60% chance of showers and a few a thunderstorms. Even though all the models were producing 5 to 10 inches of rain and showing a significant risk of severe thunderstorms. I thought that was kinda odd.




At the same time, there is another way of viewing this, forecasting weather in Florida is very hard, and when your a professional meteorologist, its always wise to go Conservative and wait a while to see how things unfold. Its far better and more professional with a forecast to be Conservative then to be "the boy who cried wolf". When that happens, nobody trusts you anymore.


Of course they are watching the models, and there are plenty of weather freaks like me in the profession that would love to see that storm season start early but they can't let that bias affect their forecast as a professional.

That should explain why it has been this way I would think.
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Quoting jeffs713:
I think another question that deserves asking...

Why are you watching TWC?
Sometimes you have to watch it just to catch up on the disastrous weather. They are good at showing that. Last week when those tornadoes were spawning, it was the only channel with any information.
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Quoting RastaSteve:


Nothing else on TV! Pretty lame shows lately on TV and the Magic weren't playing that day. Last resort.


Dude, thats desperation. I would think the "watching grass grow" channel, or "Paint Drying Today" would be more entertaining. ;)
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I think another question that deserves asking...

Why are you watching TWC?
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160. Skyepony (Mod)
DATE/TIME LAT LON CLASSIFICATION STORM
21/1745 UTC 24.2N 63.1W TOO WEAK 91L
21/1145 UTC 23.4N 62.9W TOO WEAK 91L
21/0515 UTC 23.1N 62.5W TOO WEAK 91L
20/2345 UTC 23.2N 62.0W TOO WEAK 91L
20/1745 UTC 23.0N 60.8W ST1.5 91L


I posted this earlier without the most recent line that was added since. Saw the comments "TOO WEAK??" Yesterday this time of day 91L had a tight spin. Though the higher winds were off to the NE but got points for a perfect circle on that Ascat pass we got.

Like Dr Masters has pointed out the circulation is looking poor, elongated. Check out this morning's Windsat.


Really see the next 2 days as it's window of chance. I wouldn't be surprised to see it become a named STS/TS or a depression about the time it starts moving south & then more SE~ weakening as it moves through the Bahamas, maybe pretty weak into SFL on the end of day 5. This one is crazy tenacious, being this much to watch under such shear.
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Quoting Levi32:


"Before 91L reaches Bermuda, steering currents will reverse and force 91L to the south-southwest on Saturday, into a region of higher wind shear."
Hmmm I guess I misread him, my mistake, how weird, I looked at it and thought he said otherwise. That's weird how the brain does that.
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Quoting RastaSteve:


I wouldn't have posted this I didn't hear that the other night. This is what made me think about it. She was serious and even gave examples of why not to go in a ditch. This was no mistake I can assure you of that. I think what prompted her to say that was they posted the video of the idiot in his car while a tornado was coming at him this past weekend.


Hmmm that is crazy... Well maybe they are hiring people who aren't meteorologists these days lol, who knows.... NBC did by buy the channel, so that's probably why they may have gone downhill... I don't know.
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140

WHXX04 KWBC 211742

CHGQLM

ATTENTION...NATIONAL HURRICANE CENTER



NCEP COUPLED GFDL HURRICANE MODEL FORECAST MADE FOR



TROPICAL STORM INVEST 91L



INITIAL TIME 12Z APR 21



DISCLAIMER ... THIS INFORMATION IS PROVIDED AS GUIDANCE. IT

REQUIRES INTERPRETATION BY HURRICANE SPECIALISTS AND SHOULD

NOT BE CONSIDERED AS A FINAL PRODUCT. PLEASE SEE THE TPC/NHC

OFFICIAL FORECAST.





FORECAST STORM POSITION



HOUR LATITUDE LONGITUDE HEADING/SPEED(KT)



0 23.5 62.7 280./ 7.0

6 24.0 63.2 314./ 7.0

12 24.5 63.1 20./ 4.5

18 25.2 62.8 23./ 8.0

24 25.9 62.8 356./ 7.1

30 26.4 62.8 1./ 4.2

36 26.2 62.8 180./ 1.4

42 26.0 62.6 146./ 3.1

48 25.8 62.7 203./ 1.3

54 25.4 63.1 224./ 5.3

60 25.0 63.5 223./ 6.2

66 24.4 64.3 233./ 9.5

72 23.9 65.2 240./ 9.2

78 23.7 66.1 258./ 8.7

84 23.4 66.8 251./ 7.1

90 23.3 67.6 265./ 7.0

96 23.4 68.4 276./ 7.6

102 23.6 68.9 290./ 5.4

108 24.4 68.9 1./ 7.9

114 25.2 69.3 336./ 8.4

120 25.9 69.8 322./ 8.0

126 26.5 70.2 331./ 7.7


Member Since: July 15, 2006 Posts: 171 Comments: 53835
660

WHXX01 KWBC 211849

CHGHUR

TROPICAL CYCLONE GUIDANCE MESSAGE

NWS NATIONAL HURRICANE CENTER MIAMI FL

1849 UTC THU APR 21 2011



DISCLAIMER...NUMERICAL MODELS ARE SUBJECT TO LARGE ERRORS.

PLEASE REFER TO NHC OFFICIAL FORECASTS FOR TROPICAL CYCLONE

AND SUBTROPICAL CYCLONE INFORMATION.



ATLANTIC OBJECTIVE AIDS FOR



DISTURBANCE INVEST (AL912011) 20110421 1800 UTC



...00 HRS... ...12 HRS... ...24 HRS. .. ...36 HRS...

110421 1800 110422 0600 110422 1800 110423 0600



LAT LON LAT LON LAT LON LAT LON

BAMS 24.4N 63.0W 25.2N 63.7W 25.5N 64.1W 25.1N 64.6W

BAMD 24.4N 63.0W 26.8N 59.7W 29.4N 57.7W 31.4N 55.9W

BAMM 24.4N 63.0W 25.7N 62.8W 26.6N 62.8W 26.3N 63.0W

LBAR 24.4N 63.0W 25.5N 61.9W 26.4N 60.6W 27.1N 59.0W

SHIP 35KTS 36KTS 35KTS 31KTS

DSHP 35KTS 36KTS 35KTS 31KTS



...48 HRS... ...72 HRS... ...96 HRS. .. ..120 HRS...

110423 1800 110424 1800 110425 1800 110426 1800



LAT LON LAT LON LAT LON LAT LON

BAMS 24.2N 65.9W 23.2N 70.1W 23.7N 74.6W 25.8N 77.9W

BAMD 32.4N 52.9W 30.1N 48.8W 28.3N 49.8W 26.5N 50.1W

BAMM 25.2N 63.9W 23.4N 66.2W 23.2N 68.3W 24.3N 70.4W

LBAR 27.6N 57.5W 27.3N 54.4W 26.5N 52.9W 25.8N 52.4W

SHIP 22KTS 0KTS 0KTS 0KTS

DSHP 22KTS 0KTS 0KTS 0KTS



...INITIAL CONDITIONS...

LATCUR = 24.4N LONCUR = 63.0W DIRCUR = 340DEG SPDCUR = 6KT

LATM12 = 23.4N LONM12 = 62.5W DIRM12 = 288DEG SPDM12 = 7KT

LATM24 = 23.2N LONM24 = 60.8W

WNDCUR = 35KT RMAXWD = 105NM WNDM12 = 35KT

CENPRS = 1009MB OUTPRS = 1012MB OUTRAD = 150NM SDEPTH = D

RD34NE = 105NM RD34SE = 0NM RD34SW = 0NM RD34NW = 105NM



$$
Member Since: July 15, 2006 Posts: 171 Comments: 53835
Quoting RastaSteve:


I swear I saw a couple of nights ago a lady say that on that Channel no lie. This was no mix up. I think she's on with Paul Goodman. I was shocked that she said that infact I looked over to my wife and said I can't believe I just heard that.


lol well they are always saying otherwise on there, she messed up and shoulda corrected herself, a lot of TV meteorologists must be somehow getting jobs without degrees in weather science or something.
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WTI Crude Oil
$112.19
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Quoting Jedkins01:
Why is Dr. Masters saying it will move toward Bermuda? That's not what the models say...


"Before 91L reaches Bermuda, steering currents will reverse and force 91L to the south-southwest on Saturday, into a region of higher wind shear."
Member Since: November 24, 2005 Posts: 635 Comments: 26647
Quoting jeffs713:
138. More proof that TWC has gone from decent to overhyped sensationalistic poo.


lol the TWC never said that, not sure what hes talking about
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138. More proof that TWC has gone from decent to overhyped sensationalistic poo.
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143. JRRP
Member Since: August 16, 2007 Posts: 0 Comments: 5807
Quoting RastaSteve:
WOW! Mature Nature is nothing to fool with. The funny thing is I heard on the TWC is that the safest place during a TORNADO would be in a car instead of a ditch. This will make you think twice. Again WOW! Notice the street sign stuck inside the car.

Mind you this was an EF-1 tornado that did this below.

http://www.accuweather.com/blogs/weathermatrix/st ory/48591/why-you-dont-stay-in-your-car-during-a-t ornado.asp


dude you do realize what they say on the TWC almost every day is what the NWS says, go into a ditch, not into a car. Are you sure you didn't mix that up?
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Why is Dr. Masters saying it will move toward Bermuda? That's not what the models say...
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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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