Caribbean disturbance 94L dumping heavy rains on Jamaica

By: Dr. Jeff Masters , 4:44 PM GMT on June 05, 2011

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A large, wet, and disorganized tropical disturbance (Invest 94L) continues to spread heavy rain to the Central Caribbean near Jamaica. Rain has fallen continuously at Jamaica's Kingston Norman Manley Airport since midnight, with 1.89" having fallen from midnight to noon local time. Sustained winds of 24 mph also affected Kingston between 7am and 8am this morning. Satellite-estimated rainfall amounts of 1.4" per hour occurred in ocean regions 100 miles to the southeast of Kingston this morning, and heavy rains of up to 1/2" per hour are probably affecting portions of Jamaica early this afternoon, judging by the recent increase in heavy thunderstorm activity seen on visible satellite loops. This imagery also shows a slow increase in organization of 94L in recent hours, with spiral bands beginning to develop to the southeast of the center. There is a broad, poorly-defined circulation apparent that is not well enough defined to make 94L a tropical depression. Water vapor satellite loops show a region of dry air on the west side of 94L, and this dry air is interfering with the storm's organization. However, upper air balloon soundings from Kingston and the Cayman Islands taken at 8am EDT this morning show much moister air at mid levels of the atmosphere compared to Saturday (2% humidity at 500 mb on Saturday, compared to 49% this morning at Grand Cayman), and 94L appears to be gradually overcoming its dry air issues. Wind shear remains in the moderate range, 15 - 20 knots, and is predicted by the SHIPS model to remain below 20 knots through Tuesday morning. Water temperatures in the Central Caribbean are about 1°C above average, 28 - 28.5°C, which is 2°C above the threshold needed to support development of a tropical storm.


Figure 1. Rainfall rates of up to 1.4" per hour (pink colors) were estimated by the F-15 satellite for 94L at 6:02am EDT Jun 5, 2011.

Since 94L is so large and is battling dry air, it is taking its sweet time to develop, and today's mission by the Hurricane Hunters has been cancelled. A new mission is scheduled for Monday afternoon at 2pm EDT. This morning's 06Z model runs are pretty unimpressed with 94L, with most of them showing little or no development. At 2pm EDT on Sunday, NHC gave the disturbance a 40% of developing into a tropical depression by Tuesday. If 94L stays to the south, its chances of development are greater, since a band of very high wind shear of 30 - 50 knots lies over Cuba and the southern Bahama Islands. The disturbance is expected to meander slowly westward or northward over the next two days, with Jamaica and southeastern Cuba being the primary targets for very heavy rains of 4 - 8 inches through Tuesday. Haiti and Central Cuba can expect somewhat lesser rains of 3 - 6 inches. If 94L does develop into a tropical depression and moves northwards over Cuba by Wednesday, I don't see the storm attaining hurricane strength, due to the high wind shear. The primary threat from 94L will be very heavy rains, capable of causing life-threatening flash flooding.


Figure 2. Afternoon satellite image of the Central Caribbean disturbance 94L.

Jeff Masters

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896. 7544
look at the spin just south of jamacia at 78 west could it relocate there
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Got my first drop of rain here in Houston since May 11th.
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Quoting sunlinepr:
Levi, you explained a couple of Tidbits ago, that the posible trajectory of the Invest, would depend on where the ridge from the north interacted with 94L... According to actual observations, is there a tendency to favor it to enter the GOM?


I've been mentioning for a while that the GOM would be closed to this system during most of its playtime in the Caribbean, but that if it sat in the Caribbean long enough, meaning into the middle or latter part of this week, the pattern would flatten out and a break could open in the ridge, allowing the system to have access to the Gulf of Mexico. That is starting to appear more likely today, as the system's motion is westward and fully caught in the flow around the eastern U.S. ridge. It is unlikely that it will be pulled northeast into the west Atlantic trough at this point, and given that it doesn't really have anywhere else to go fast, it will likely be around for the ridge to break down and allow it to drift north or northwest into the eastern Gulf of Mexico or Florida, bringing drought relief by late this week.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting Drakoen:

Well in general yes there is. The low is quite broad. Also take a look at buoy 42057. It is reporting winds out of the NNE which means the low is east of that buoy and not west of which is where they have placed it. If the low was west of the buoy the buoy would be reporting winds out of the southwest.


Surely very broad and I agree with you. You think they may be triangulating the broad low to a mean center?? Hard to imagine they would do that but, I can't see any other reason why they would place it in that location based on obs.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting TxHurricanedude11:

llc a lil bit north of your circle


yea, im not really pulling hairs...just general locations...this this is an invest...ill worry bout being more precise when we get a td....lol
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Quoting Mrsenseofhumor:
Is WUBA still around?


They hooked up their double-wide trailers and left town.
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The persistence of the Jamaican circulation makes me wonder if that will take over.
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Quoting eliteforecaster:
thanks levi.

Would less shear in the epac also be a reason? Shear seems to be a very frequently cited reason for lack of development in the Atlantic, but I usually don't see that being the case in the epac. Is my assumption true, or is shear about equal in both basins?

Also, why does the epac have ne winds meeting sw winds, while the Atlantic has se winds meeting ne winds?


Regarding wind shear, the EPAC has less than the Atlantic in the early and late season, but can have more than the Atlantic in the height of the season due to the upper easterlies that come from the monsoonal circulation over Mexico. These easterly upper winds are usually said to reduce wind shear, but that's in the Atlantic where the surface winds are predominantly easterly as well. In the eastern Pacific during the height of the season, the surface winds are predominantly southwesterly or nearly calm farther north, which results in stronger vertical wind shear, since the upper winds are in the opposing direction.

As to why there is a SW flow in the EPAC but not the Atlantic, it is due to the monsoon trough. This is a heat-induced trough which develops over central America during the summer due to solar heating which lowers the surface pressure. Wind rushes out of the southwest from the ocean towards this low pressure, meeting the northeast trades from the Caribbean, thus forming the monsoon trough.

The Atlantic does not have a landmass like central America, so much of the MDR consists of a regular ITCZ with SE trades meeting NE trades. However, there is a monsoon trough near and west of Africa, due to the African monsoonal circulation. Again, summer heating reduces the surface air pressure over Africa, drawing southwesterly winds off of the tropical Atlantic. You can see this on summer ASCAT passes.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting Levi32:
The surface circulation is clearly evident here.

Correct.
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Quoting CyclonicVoyage:


That's where I had it. I found it odd they placed it there however, there is a low level circulation present at that location. Had to decipher but, it's there.
Well in general yes there is. The low is quite broad. Also take a look at buoy 42057. It is reporting winds out of the NNE which means the low is east of that buoy and not west of which is where they have placed it. If the low was west of the buoy the buoy would be reporting winds out of the southwest.
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94L Rainbow Floater



WV

Member Since: July 3, 2005 Posts: 426 Comments: 128645
Quoting jitterboy:
Keeper of the.. I know this is off topic, but I was wondering if you would be so kind to post the visible GEOS centered on Colorado. I is super smokey here and I was wondering which fire it was coming from. Thanks in advance


Here you go, idk if you can see where its from though.

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94L Enhanced Infrared (IR) Imagery (4 km Mercator)


Member Since: July 3, 2005 Posts: 426 Comments: 128645
Quoting CyclonicVoyage:
SSD just moved the low out to 17.1N 81.2W and lowered the pressure to 1006.


splitting the difference...it seems...
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Levi, you explained a couple of Tidbits ago, that the posible trajectory of the Invest, would depend on where the ridge from the north interacted with 94L... According to actual observations, is there a tendency to favor it to enter the GOM?
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Quoting Mrsenseofhumor:


Sure Mr Fish Curtains plays most of them characters.


He's the brunt.........
;)
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Quoting jitterboy:
Keeper of the.. I know this is off topic, but I was wondering if you would be so kind to post the visible GEOS centered on Colorado. I is super smokey here and I was wondering which fire it was coming from. Thanks in advance
here is what i have

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>

94l's circulations...
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Quoting Drakoen:

The low position is further east than what they are showing by about 75 miles.


That's where I had it. I found it odd they placed it there however, there is a low level circulation present at that location. Had to decipher but, it's there.
Member Since: January 30, 2010 Posts: 0 Comments: 3259
Quoting eliteforecaster:
ok, so let me get this straight, this was my interpretation of diurinal cycles over the ocean:

During the day time, solar heating increases the atmosphere such that the atmosphere aloft is warmer than the layer of the atmosphere directly at the surface which remains cooler due to the ocean's cooler temperature. As a result, instability decreases and we see the convective dmin. During nighttime, the atmosphere above the surface layer cools, while the layer of atmosphere closest to the ocean cools slightly but remains relatively warm due to the oceans specific heat properties which allow it to experience minimal heat fluctuations. As a result, the atmosphere is cooler aloft and warmer at the surface, increasing instability and therefore we see the convective dmax.

Now, what you're saying is the pressure over the ocean reaches a minimum during the convective dmax, but also during the afternoon when the atmosphere above the surface is warmest as a result of the expanding air?

Also did you see my post in response to your post on greater activity in the epac?



You have the convective diurnal cycle correct. The pressure tides are driven by a wave in the upper atmosphere that follows the sun (the sun's position directly overhead). The highest amplitude cycle has a lowest pressure at 4am, which is also convective DMAX. The secondary period minimum at 4pm I believe is a secondary wave fluctuation in the upper atmosphere. Such a fluctuation will not necessarily control the instability of the atmosphere at that time of day, since the convective DMIN at that time is the dominant force.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting galvestonhurricane:


Thanks, I know all of us in Houston/Texas/S. Florida appreciate that.
My magical fairy dust should help with that in the coming months.
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from WKRG FB

Uriah Al, has been hit. 10 to 15 homes are damaged.
56 minutes ago · Like ·

Mary Pettis Uriah??? Tornado??
54 minutes ago · Like

Trisha Davis Dont know if it was tornadoes or straight line winds, its right out side of Uriah town on 21. Rays Fruit stand has nothing left but the Freezer. Reports of about 1/4 mile wide hit with 10 to 15 homes with moderate to sever damage.
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Quoting Levi32:


It appears to be mid-level, as the rotation is noticeable in the milky-looking clouds, which are either cirrus or mid-level debris. Additionally, the surface flow observable in the clear areas does not support the presence of a surface circulation stacked underneath the mid-level vortex, as the surface flow directly south of the western tip of Jamaica is out of the southwest, which implicates a surface low to the WSW of Jamaica.

Fantastic!
Much appreciated.
Member Since: October 24, 2005 Posts: 0 Comments: 24388
Quoting Mrsenseofhumor:


They were a fun group...


We have a new cast of characters now. Kind of like how SNL does things. :|
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Quoting CyclonicVoyage:
SSD just moved the low out to 17.1N 81.2W and lowered the pressure to 1006.
The low position is further east than what they are showing by about 75 miles.
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Quoting Drakoen:

It is mid level, above the surface layer. You have to look underneath and around this mid level spin to get an idea of the surface. The surface is represented by those thin, streaking clouds and if you look west of the convection you an get an idea of how this flow is moving to determine where the surface center is.

OK, Excellent !.
Thanks Drak.
Member Since: October 24, 2005 Posts: 0 Comments: 24388
Quoting PlazaRed:
Quoting:- 832. galvestonhurricane

You really do have my deepest sympathies and I sincerely do hope you get some rain ASAP and those temps drop by at least 15/F in your area.
I normally live in southern Spain and we don't normally get any rain from end of April till end of September so that's about 5 months with the temps at about 90-100/F every day, its hell and I know better than most what you are going through, I don't think this scenario can go on much longer for you.
You should get something out of the season soon, last year must have been an anomaly and with the La Nina as well.


Thanks, I know all of us in Houston/Texas/S. Florida appreciate that.
Member Since: June 18, 2010 Posts: 0 Comments: 539
Quoting pottery:
So what is that vortex just west of due south of Kingston?
Serious question, it's very pronounced on the last couple of frames...
Check it again.


It appears to be mid-level, as the rotation is noticeable in the milky-looking clouds, which are either cirrus or mid-level debris. Additionally, the surface flow observable in the clear areas does not support the presence of a surface circulation stacked underneath the mid-level vortex, as the surface flow directly south of the western tip of Jamaica is out of the southwest, which implicates a surface low to the WSW of Jamaica.
Member Since: November 24, 2005 Posts: 635 Comments: 26654
Quoting Mrsenseofhumor:


They were a fun group...



yup oh well life gos on has we will go on
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SSD just moved the low out to 17.1N 81.2W and lowered the pressure to 1006.
Member Since: January 30, 2010 Posts: 0 Comments: 3259

Quoting pottery:
So what is that vortex just west of due south of Kingston?
Serious question, it's very pronounced on the last couple of frames...
Check it again.
It is mid level, above the surface layer. You have to look underneath and around this mid level spin to get an idea of the surface. The surface is represented by those thin, streaking clouds and if you look west of the convection you an get an idea of how this flow is moving to determine where the surface center is.
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Quoting Levi32:


There's a difference between "DMIN" and diurnal pressure cycles. The former is what Hurry was talking about, with the air being the warmest during the day, decreasing the instability between the warm ocean surface and the atmosphere above.

Diurnal pressure cycles have a minimum pressure in the afternoon which is thought to be caused by solar heating of the upper atmosphere, which lowers the pressure at the surface. There is also a secondary diurnal cycle which has a pressure minimum just before sunrise.
ok, so let me get this straight, this was my interpretation of diurinal cycles over the ocean:

During the day time, solar heating increases the atmosphere such that the atmosphere aloft is warmer than the layer of the atmosphere directly at the surface which remains cooler due to the ocean's cooler temperature. As a result, instability decreases and we see the convective dmin. During nighttime, the atmosphere above the surface layer cools, while the layer of atmosphere closest to the ocean cools slightly but remains relatively warm due to the oceans specific heat properties which allow it to experience minimal heat fluctuations. As a result, the atmosphere is cooler aloft and warmer at the surface, increasing instability and therefore we see the convective dmax.

Now, what you're saying is the pressure over the ocean reaches a minimum during the convective dmax, but also during the afternoon when the atmosphere above the surface is warmest as a result of the expanding air?

Also did you see my post in response to your post on greater activity in the epac?

Quoting eliteforecaster:
thanks levi.

Would less shear in the epac also be a reason? Shear seems to be a very frequently cited reason for lack of development in the Atlantic, but I usually don't see that being the case in the epac. Is my assumption true, or is shear about equal in both basins?

Also, why does the epac have ne winds meeting sw winds, while the Atlantic has se winds meeting ne winds?
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Hi everyone could 94l possibly bring us rain in fla. panhandle?? and if so what possible intensity would it be?? thanks for any input
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Quoting washingtonian115:
Looks like an organizing tropical cyclone to me.



yup
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Quoting Mrsenseofhumor:
Is WUBA still around?


nop
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Quoting:- 832. galvestonhurricane

You really do have my deepest sympathies and I sincerely do hope you get some rain ASAP and those temps drop by at least 15/F in your area.
I normally live in southern Spain and we don't normally get any rain from end of April till end of September so that's about 5 months with the temps at about 90-100/F every day, its hell and I know better than most what you are going through, I don't think this scenario can go on much longer for you.
You should get something out of the season soon, last year must have been an anomaly and with the La Nina as well.
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Quoting Stormchaser2007:
Looks like an organizing tropical cyclone to me.
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Quoting Levi32:
The surface circulation is clearly evident here.

So what is that vortex just west of due south of Kingston?
Serious question, it's very pronounced on the last couple of frames...
Check it again.
Member Since: October 24, 2005 Posts: 0 Comments: 24388
So 94L's current pressure is 1007mb? Either way well likely see it's real central pressure from the bouy Levi is showing, probably 1006 mb or so... No tellin...
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Levi32..well can you give me a more specific explanation and overview as to what pattern over the United States is best conducive for U.S hurricane landfalls and what makes this year's setup different from last year's? I am just confused on the whole trough-ridge pattern over the Atlantic
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Keeper of the.. I know this is off topic, but I was wondering if you would be so kind to post the visible GEOS centered on Colorado. I is super smokey here and I was wondering which fire it was coming from. Thanks in advance
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847. xcool


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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.