97L fizzles; new Bahamas disturbance develops

By: Dr. Jeff Masters , 2:17 PM GMT on July 21, 2009

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A strong tropical wave (97L), now located just south of Puerto Rico, has grown disorganized today. Sustained winds as high as 26 mph were observed on Barbados, and 35 mph winds were observed on St. Lucia yesterday when 97L passed through the Lesser Antilles Islands. Wind gusts to 45 mph and heavy rain can be expected in the Dominican Republic and Puerto Rico this afternoon, and in Haiti and the southeastern Bahama Islands on Wednesday. However, 97L is under too much wind shear to develop, and shear will remain in the high 25 - 35 knot range over the disturbance over the next two days.


Figure 1. Today's disturbances to watch.

A new tropical disturbance has formed north of the central Bahama Islands, about 600 miles east of Miami. The thunderstorm activity is not yet very intense, but does cover a moderately large area. This morning's QuikSCAT pass showed winds of 20 - 25 mph, and no evidence of a circulation trying to form. This region is under about 20 - 25 knots of wind shear, and has the potential for some slow development over the next few days as it moves slowly northwards. The GFS and ECMWF models hint at the possibility that this system may attempt to organize into a tropical depression by Friday, off the coast of North Carolina.

I'll have an update Wednesday.

Jeff Masters

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1157. Ossqss
Looks like the Bahamas are going to become Ovoviviparous. LoL
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Quoting Weather456:
I just notice this. Am I late or what?



Gasp.. your late.. thats not good :)
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Quoting Weather456:
I just notice this. Am I late or what?



the 2 yellow circles have been there since 8am this morning
I just notice this. Am I late or what?

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AOI

AOI

AOI
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1151. CUBWF
Looks by radar the llc is moving again nw and living behind the convection. 17.4 68.5w
Quoting Weather456:


I think vorticity remain the same for the Bahamas system but has become elongated. 97L vorticity has decrease.


well let me ask you something 456 that hasnt been touched on. You said 97L will likely split like the wave before it did. The northern portion is likely to help spark development in the Bahamas in a few days

My question is the southern portion you said would continue west, if that anticyclone stays put in the West Caribbean, why couldnt the southern part of 97L develop?
Quoting BurnedAfterPosting:


looks to be hitting South America to me

the top ball of convection is trying to lift out
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting weatherwatcher12:
lifting out of the ITCZ


looks to be hitting South America to me
Quoting reedzone:
HOWEVER, vorticity has decreased in both 97L and the Bahamas invest.

http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8vor4.html


I think vorticity remain the same for the Bahamas system but has become elongated. 97L vorticity has decrease.
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lifting out of the ITCZ
Member Since: May 16, 2009 Posts: 1 Comments: 1231
it needs to be noted that no development is going to occur with either area until Thursday or Friday; yes more patience is needed lol
Quoting BurnedAfterPosting:
many times these systems in the Bahamas go through these phases, it looked decent earlier, now it looks like crap lol, not really due to diurnal phases

Starting tomorrow it should start to organize better



That's why I'm not expecting anything until Thursay. This system will go up and down as it develops so it should take a while.
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Anticyclone strengthens and is now in the Western Carribean again.
Member Since: July 1, 2008 Posts: 13 Comments: 7396
Quoting Weather456:
Alex 2004, interesting genesis here.

Three distinct weather systems may have played a role in the genesis of Alex. On 26 July, shower activity increased several hundred miles to the east of the northwestern Bahamas. This activity was associated with a weak surface trough, likely of mid-latitude origin. Disorganized showers persisted just to the east of the Bahamas, in the diffluent region to the east of an upper-level low, for the next couple of days. On 28 July, when a tropical wave reached the area, the extent and organization of the convection began to increase. Analyses show that a broad area of surface low pressure formed early on 30 July just northeast of the central Bahamas. The low moved northwestward and over the next 36 hours the circulation slowly became better defined. By 1800 UTC 31 July, when the low center was located about 175 n mi east of Jacksonville, the system had enough convective organization to be classified as a tropical depression.


Very similar to the scenerio we have now
HOWEVER, vorticity has decreased in both 97L and the Bahamas invest.

http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8vor4.html
Member Since: July 1, 2008 Posts: 13 Comments: 7396
many times these systems in the Bahamas go through these phases, it looked decent earlier, now it looks like crap lol, not really due to diurnal phases

Starting tomorrow it should start to organize better
Alex 2004, interesting genesis here.

Three distinct weather systems may have played a role in the genesis of Alex. On 26 July, shower activity increased several hundred miles to the east of the northwestern Bahamas. This activity was associated with a weak surface trough, likely of mid-latitude origin. Disorganized showers persisted just to the east of the Bahamas, in the diffluent region to the east of an upper-level low, for the next couple of days. On 28 July, when a tropical wave reached the area, the extent and organization of the convection began to increase. Analyses show that a broad area of surface low pressure formed early on 30 July just northeast of the central Bahamas. The low moved northwestward and over the next 36 hours the circulation slowly became better defined. By 1800 UTC 31 July, when the low center was located about 175 n mi east of Jacksonville, the system had enough convective organization to be classified as a tropical depression.
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New Shear map shows marginal to a bit unfavorable conditions, probably the reason for the convection staying in tact for the most part. Shear continues to increase in the Bahamas though, decreasing in the Carribean.

http://cimss.ssec.wisc.edu/tropic/real-time/atlantic/winds/wg8shr.html
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Member Since: May 16, 2009 Posts: 1 Comments: 1231
New shear map. Conditions continuing to improve around 97L.
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Latest Puerto Rico Radar
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting Weather456:


Ok. But read the header, the rainfall data is ending July 20. Some caribbean sations stop reporting around 8 pm (including mines). So the rainfall maybe was higher. And i always inlcude in my reports regardless of development, such and such is possible. And why is this of such importance? the NHC, NWS or Met offices in the respect islands can effectively warn their people without reading my blog.

The problem here probably arises from the fact that these readings are taken from the airports which are quite often on the "dry side" of these islands which leads to the wrong picture being painted a lot of the time. It is still unbelievable that during that period on Monday Dominica is reported to have received only 0.25" when where I live had 3.45" in the same period.
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Quoting CycloneOz:


F combined with S creates a new term with almost the same ramifications as the single word "fizzle." :)


I'm learning!
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Quoting KoritheMan:


Yeah, and this is definitely a climatologically favored spot for tropical cyclogenesis. Alex in 2004, Franklin 2005, Beryl in 2006, Chantal in 2007, Cristobal in 2008, all formed from a trough of low pressure in the vicinity of the Bahamas in mid to late July.

Fortunately, climatology also favors a sharp recurvature.


That's a good way of looking at it.
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Nrt
Quoting nrtiwlnvragn:


Zoo

Latest Area Forecast has backed off of heavy rain, but with the tropics that may change.


didn't see that yet - good I hate to get rained on when I'm out with clients during the day.
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Quoting Weather456:
This system is much similiar to 91L/Td 1, except there wasn't a tropical wave invovled.


Yeah, and this is definitely a climatologically favored spot for tropical cyclogenesis. Alex in 2004, Franklin 2005, Beryl in 2006, Chantal in 2007, Cristobal in 2008, all formed from a trough of low pressure in the vicinity of the Bahamas in mid to late July.

Fortunately, climatology also favors a sharp recurvature.
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Quoting Weather456:


Most likely, tropical wave reaches you guys by Wednesday and LLC behind it roughly crosses the island, so yea, squally weather in store for the island, which is typical tropical wave weather.

thanks
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting BurnedAfterPosting:


A High building over an area would give it very favorable conditions and would aid development, your meteorologist is mistaken


That's why I didn't reply because that's a contradiction there.
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Quoting stormsurge39:
Is there high pressure building over bahamas??


maybe he meant pressures were still high in the Bahamas?
high pressure doesnt push it away from it?
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F combined with S creates a new term with almost the same ramifications as the single word "fizzle." :)
Member Since: August 26, 2006 Posts: 10 Comments: 3753
Quoting reedzone:
My forecast for right now..

Photobucket



right on
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Quoting KoritheMan:


About what I am predicting.


That's what it pretty much looks like to me, they both forma big mess, then shear lowers on Thursday and develops a new feature.
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Is there high pressure building over bahamas??
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Quoting stormsurge39:
I just saw the weather and the meterologist said there was a high building over the AOI in the bahamas and will not allow it to develope.


A High building over an area would give it very favorable conditions and would aid development, your meteorologist is mistaken
This system is much similiar to 91L/Td 1, except there wasn't a tropical wave invovled.
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Quoting reedzone:
My forecast for right now..

Photobucket


About what I am predicting.
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Quoting weatherwatcher12:

So weather456 do you expect any impacts in Jamaica because local mets are predicting strong gusty winds and heavy rain


Most likely, tropical wave reaches you guys by Wednesday and LLC behind it roughly crosses the island, so yea, squally weather in store for the island, which is typical tropical wave weather.
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My forecast for right now..

Photobucket
Member Since: July 1, 2008 Posts: 13 Comments: 7396
Quoting Weather456:


Let me clarify, the wave axis it self is forecast to continue west. The energy associated with the northern section of the wave may add to the mix over the Bahamas and aid in some genesis. Now shear is expected to be favorable over the SW N ATL by Thursday, so by then you might see the orignial wave axis associated with 97L over the W Caribbean, independent of the energy it contributed to the genesis of a possible new feature.

For example the wave axis associated 97L is near 82W by thursday with a possible trough to the N over the SW ATL


So weather456 do you expect any impacts in Jamaica because local mets are predicting strong gusty winds and heavy rain
Member Since: May 16, 2009 Posts: 1 Comments: 1231
Quoting Weather456:


by 6:40 EDT/AST


Cool, thanks :)
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Quoting reedzone:
Anybody know when the next shear map comes out?


by 6:40 EDT/AST
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I just saw the weather and the meterologist said there was a high building over the AOI in the bahamas and will not allow it to develope.
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So far today in the Turks & Caicos we've only had one significant squall. We are in the gap between the two blobs.... but I think things will go Bump in the night.
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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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