Tropical depression forming over the Bahamas

By: Dr. Jeff Masters , 1:29 PM GMT on July 22, 2010

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A tropical wave (Invest 97L) over the eastern Bahama Islands has developed a closed circulation at the surface, and has become a tropical depression or tropical storm. Here is the text of the Special Tropical Weather Outlook from NHC at 8:25am EDT today:

Visible satellite images and observations from the Bahamas indicate that the area of low pressure in the southeastern Bahamas has become better organized and a closed circulation has formed. Advisories on a tropical depression or a tropical storm will be initiated at 11 am EDT...1500 UTC today. This advisory will likely include tropical storm watches and warnings for portions of the Bahamas and southern Florida.

Satellite images of 97L show a modest area of heavy thunderstorms that have slowly increased in intensity and areal coverage this morning. Water vapor satellite loops show a large area of dry air lies to the west of 97L, over Florida. This dry air is associated with a large upper-level low pressure system that is moving west at about the same speed 97L is. The counter-clockwise flow of air around the upper low is bringing about 20 knots of wind shear to 97L. Surface observations in the Bahamas and several nearby ships have shown top winds in 97L of up to 35 mph, so the storm is close to the 40 mph winds needed to be classified as a tropical storm.


Figure 1. Water vapor satellite image showing dry air (brown colors) associated with the upper-level low over Florida. Image credit: NOAA/NESDIS.

Track Forecast for 97L
The storm is in a fairly straightforward steering current environment, and 97L should progress steadily to the west to west-northwest through Saturday. This will bring the storm ashore over the Florida Keys or South Florida on Friday, and into the Gulf of Mexico on Saturday. The latest set of model runs from 2am EDT (6Z) had the advantage of having data from a flight of the NOAA jet last night, so we have higher confidence than usual in the track of 97L over the next two days. The location of 97L's final landfall along the Gulf of Mexico coast has the usual uncertainties for 3 - 4 days, with the various models calling for landfall somewhere between the upper Texas coast and the Florida Panhandle coast. Given the uncertainties, the move halt operations in the Deepwater Horizon blowout recovery effort are probably wise.

Intensity Forecast for 97L
The primary detriment to development of 97L for the next three days will be the presence of the large upper-level low to its west. As long as this low remains in its present location, relative to 97L, it will bring wind shear of about 20 knots and dry air into the storm. This will limit the intensification potential of 97L to no more than about 10 - 20 mph per day. If the upper-level low picks up speed and pulls away from 97L, the storm may be able to intensify at a faster rate. None of the computer models is calling for that to happen, but it is possible. I put the odds of 97L making it to hurricane strength in the Gulf of Mexico at 20%.

98L
An area of disturbed weather (98L) has developed in the Gulf of Mexico's Bay of Campeche. This system is under a low amount of shear, 5 - 10 knots, and may barely have enough time to organize into a tropical depression before making landfall along the Mexican coast a few hundred miles south of the Texas border on Friday.

I'll have an update after NHC releases their 11am advisory package.

Jeff Masters

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Quoting Jeff9641:
The latest NAM has shifted north and is calling for S FL to panhandle impact.
Intensity?
Member Since: Posts: Comments:
370. IKE
refresh....refresh....refresh....sip of coffee....refresh...refresh....
Member Since: June 9, 2005 Posts: 23 Comments: 37858
Are the HH scheduled to go out today?
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Quoting PensacolaDoug:



How true!


Doug.. If it comes yur way we will expect some webcam action shots of you as it comes in!!!1
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Quoting DestinJeff:


as a joke once the NHC should post the track graphic 15 times one below the other.

NO bad idea we need the blog space for when the real insanity begin
Wow 98L is really getting its act together looks very organized.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Quoting hydrus:
97L is in the midst of all those good sized islands. Could this slow the organization?


Navy site already has it as TD 3 for the past hour.
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I would be surprised if we do not have Bonnie by noon today.
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Quoting gulfbreeze:
If you live in Pensacola or Gulf Breeze you dodn't!!



How true!
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Quoting StormW:


Yeah...we'll get 50 posts of the first advisory.
97L is in the midst of all those good sized islands. Could this slow the organization?
Member Since: September 27, 2007 Posts: 1 Comments: 21492
359. 900MB
Storm-
The ULL seems to be moving at least twice as fast as pre-Bonnie.
Looks like the ULL might actually be moistening up the dry air as well. Do you see the dry air and shear waning here?
Member Since: June 11, 2006 Posts: 0 Comments: 684
We have a new "dot" of strong convection building at the tip of the island.
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Quoting pensacolastorm:


Why does everyone forget Ivan?
If you live in Pensacola or Gulf Breeze you dodn't!!
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Quoting hurrkat05:
tropic freak the ssts are running 84 or of fla and further out in the gulf 86,,,yesthere is strong shear and some dry air in the gom where bonnie is headed..


I disagree with you but thats ok. Shear tendencies show that shear has been dropping a little over the past 24 hours in the GOM.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
No doubt! Bonnie...
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Quoting jasoniscoolman2010x:
its time to hit F5 ON THE NHC PAGE LETS SEE IF WE HAVE TROPICAL D YET.

we've had one for 3 hours
Quoting 900MB:
Poll time!

a- TD is declared
b- Bonnie is declared


A
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349. 900MB
Quoting reedzone:


Looks more like a TD right now, recon should find stronger winds which should upgrade to TS by 5 p.m.


I'll go with that, although given Gulf interests and close proximity to US, it wouldn't surprise me to see a TS sooner. Looks like a TS on Sat.
Member Since: June 11, 2006 Posts: 0 Comments: 684
"The track as far as strength of the system should be about the same, unless it gets strong enough to be steered by the deep layer mean. Right now, shallow and mid layer are pretty much the same. Again, once this becomes better organized, steering will have to be reassessed."

Pay heed to StormW's words. Watch the storm, the models are just that.
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Quoting stormchic:

Hi Miami,
I live in southern Fl.(Homestead)do you think we will also be under the TS warnings?I enjoy your input on the tropics...thanks! :-)
Yes I do believe south Florida will be under a tropical storm warning from the Dry Tortugas to Fort Lauderdale. Just a "guesstimate" LOL!
Member Since: September 2, 2009 Posts: 130 Comments: 21194
Navy site link, but no data.

Link
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Quoting THEBIGSTORM:
And the predictions for Tampa Bay are.......???

Question: When was the last time Tampa Bay was directly hit? And what kind of atmospheric armor do we have?


The biggest problem for Tampa Bay would be this...if the oil gets to the Tampa Bay seawater desalination plant caused by this Storm...
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The Navy site has listed it as TD 3 for the past hour, but no data on it yet. And the cimss is still down.
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Quoting TampaSpin:
I now believe we have a better than 50% chance Bonnie becoming a Hurricane just before South Florida......and who knows what it will become in the GOM .....OH BOY!



Good morning !!!
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Quoting MiamiHurricanes09:
The Bahamas and south Florida will likely be under tropical storm warnings... I'm also eagerly awaiting the cone of uncertainty.

Hi Miami,
I live in southern Fl.(Homestead)do you think we will also be under the TS warnings?I enjoy your input on the tropics...thanks! :-)
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Quoting CybrTeddy:


0.000000001% chance of ever happening.

Add a few more Zero's.
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Quoting fmbill:


Getting some nice symmetry, too.


Like Isabel.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Thanks Dr. Masters and Storm!
Weather456, I hope your safe and look forward to your input.
Good morning everyone!I'm keeping my eye on this one cause it's been very persistent thus far.Whether it's storm or huricane, it's bound to negatively affect someone's property or well being. Therefore, we should all be prepared and take heed to all warning and watches placed in one's area. Just wanted to rant before it got too chaotic in here!Back to lurking...
Member Since: June 21, 2010 Posts: 0 Comments: 61
The momentum in increasing intensity continues. Higher cloud tops are showing up now. It should be Bonnie by now.

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Quoting PensacolaDoug:




So? A whole bunch of my posts, and I'm sure other peoples too don't get responded to. Develope some thicker skin. It'll serve you well.


As for the poll.

Bonnie I believe. But Iv'e been wrong plenty of times before!


40mph winds have been reported in the Bahamas.
Member Since: September 2, 2006 Posts: 110 Comments: 6878
Quoting tea3781:
Do you think that the COC will relocated itself under the deepest convection?


Where ever the red dot goes.

Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting CybrTeddy:
-80C cloudtops starting to pop up in TD3.


Getting some nice symmetry, too.
Member Since: May 27, 2008 Posts: 0 Comments: 461
Quoting largeeyes:
Wonder if this ridge is gonna protect us in the the Presslina's all summer...
I have said this for decades. The pressalina,s are never safe. If its not one thing, its another, if its not that, its something else, whether it be tornadoes, flooding, mid-latitude cyclones or hurricanes. Never safe.
Member Since: September 27, 2007 Posts: 1 Comments: 21492
Quoting tropicfreak:


Like on your avatar.
LOL! Coincidentally, yes. But without Andrew's intensity. Thank you.
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Hot towers going up?
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Because of the developments with the storm, the National Hurricane Center said they will likely begin Tropical Depression or Tropical Storm advisories at 11 a.m. which will probably include tropical storm watches and warnings for portions of the Bahamas and South Florida.
Link
Member Since: October 30, 2007 Posts: 0 Comments: 270
Quoting THEBIGSTORM:
And the predictions for Tampa Bay are.......???

Question: When was the last time Tampa Bay was directly hit? And what kind of atmospheric armor do we have?


It would be departing land when over TBW. Worst case, what we saw when frances when it did the same, but it would have to go N of TBW for that. I think it goes south of TBW. I expect 4-5 in rain, 25-30mph winds offshore, and a lot of overblown hype here and on the TV news.
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Bonnie will be steered to the west or slightly north of west due to the Strong High Pressure system
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Quoting hurrkat05:
just like i been saying bonnie can't intensify with the low to the west and the shear 30-40 knots..also the dry air thats going to be sucked into the system will disrupt bonnie.....bonnie will be no more then a weak tropical storm and as long as the shear stays around dr i have to disagree with you i give bonnie no chance of becoming a hurricane in the gom...


Well, he finally got a prediction right: No more than 10 min prior to his post, he said

"...im sure when dr masters comes on her will set all you straigh whats ahead for tropical storm bonnie once she gets close to the keys...then we will have people arguibg with him ...lol well this is a weather blog i think..."
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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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