93L slow to develop, but bringing heavy rains to Haiti

By: Dr. Jeff Masters , 1:50 PM GMT on June 22, 2010

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A modest region of intense thunderstorms (Invest 93L) is over the central Caribbean, a few hundred miles south of Hispaniola. This disturbance has the best chance to become Tropical Storm Alex of any system we've seen so far this year. We don't have any buoys near 93L, but pressures at the ground stations surrounding the storm are not falling. A pass of the ASCAT satellite over the Central Caribbean at 9:45 pm EDT last night revealed a modest wind shift associated with 93L, but nothing at all close to a surface circulation. Top surface winds seen by ASCAT were 15 - 20 mph. Water vapor satellite loops show that 93L is embedded in a large region of moist air. The atmosphere over the Caribbean has moistened over the past day, which should aid development of 93L. Wind shear is a low 5 - 10 knots. The high wind shear associated with the strong winds of the subtropical jet stream are over the northern Caribbean, too far north to interfere with development, but close enough to provide good upper-level outflow for the storm. Visible satellite loops show high level cirrus clouds streaming away from 93L to the northeast, evidence of the upper-level outflow channel that is developing to the storm's north. Sea Surface Temperatures are plenty warm, a record 29 - 30°C. The Madden-Julian oscillation (MJO) currently favors upward motion over the Caribbean, which will act to increase the chances of tropical storm formation this week. The Madden-Julian oscillation is a pattern of enhanced rainfall that travels along the Equator from west to east. The pattern has a wet phase with large-scale rising air and enhanced thunderstorm activity, followed by a dry phase with large-scale sinking air and suppressed thunderstorm activity. Each cycle lasts approximately 30 - 60 days. When the Madden-Julian oscillation is in its wet phase over a hurricane-prone region, the chances for tropical storm activity are greatly increased. The main negative for 93L continues to be lack of spin. The University of Wisconsin 850 mb relative vorticity analysis is showing that spin at 850 mb (roughly 5,000 feet in altitude) has increased over the past day, but 93L needs to acquire additional spin before it can grow more organized. I speculate that it is this lack of spin that contributed to the loss of much of 93L's heavy thunderstorm activity last night. The storm is now going through a cycle where it is building another respectable mass of heavy thunderstorms, and the increased inflow of low-level air that will feed these thunderstorms will likely enhance 93L's spin today. The Hurricane Hunters are on call to investigate 93L on Wednesday afternoon.


Figure 1. Morning visible satellite image of the central Caribbean disturbance 93L.

Forecast for 93L
NHC is giving 93L a 40% chance of developing into a tropical depression by Thursday morning, which is a reasonable forecast. Given the storm's current lack of spin and relatively modest amount of heavy thunderstorms, the earliest I'd expect 93L to become a tropical depression would be Wednesday afternoon, with Thursday more likely. Wind shear is expected to be low, less than 10 knots, over the central and western Caribbean this week. Water temperatures will be warm, dry air absent, and the MJO favorable. I don't see any major impediments to the storm becoming a tropical depression by Thursday, and it is a bit of a surprise to me that the computer models have been reluctant to develop 93L. The GFS, NOGAPS, and UKMET models do not develop 93L, and the ECMWF model doesn't develop 93L until after it crosses the Yucatan Peninsula and enters the Gulf of Mexico in a about a week. The current (2am EDT) run of the GFDL model predicts 93L will be a weak tropical storm in the Gulf of Mexico in five days; its previous run had 93L as a major hurricane in the Gulf. Given all this model reluctance and the current disorganization of 93L, I give the storm a low (less than 20% chance) of becoming a hurricane in the Caribbean. Expect 93L to bring flooding rains of 3 - 6 inches to Jamaica, eastern Cuba, and southwestern Haiti today through Wednesday. These rains will spread to the Cayman Islands and central Cuba by Thursday, and western Cuba and Mexico's Yucatan Peninsula on Friday. The current run of the SHIPS model has 93L slowing down late this week to a forward speed of just 6 knots (7 mph) from its current speed of about 10 mph, in response to a weakening in the steering currents. A trough of low pressure is expected to swing down over the Eastern U.S. early next week. If this trough is strong enough and 93L develops significantly, the storm could get pulled northwards and make landfall along the northern Gulf of Mexico coast in the oil spill region. This is the solution of the Canadian GEM model. If 93L stays weak and/or the trough is not so strong, the storm would get pushed west-northwestwards towards the Texas coast. This is the solution of the ECMWF model. The amount of wind shear in the Gulf of Mexico next week is highly uncertain. There is currently a band of high shear near 30 knots over the Gulf, and some of the models predict this shear will remain over the Gulf over the next 7 - 10 days. However, other models predict that this band of high shear will retreat northwards and leave the Gulf nearly shear-free. The long-term fate of 93L remains very murky. My main concerns at this point are the potential for 3 - 6 inches of rain in Haiti over the next two days, and the possibility 93L could become a hurricane in the Gulf of Mexico next week.

Elsewhere in the tropics
None of the reliable computer models is calling for tropical cyclone formation elsewhere in the Atlantic over the next seven days.

Floods in China and Burma kill over 250
The deadliest and most destructive weather-related disaster on the planet so far this year is occurring in southern China and northern Burma, where a week of heavy rains has caused flooding that has claimed over 250 lives. The heavy rains and floods ravaging 10 southern Chinese provinces had killed 199 and left 123 missing as of 11:00 a.m. Tuesday, a Ministry of Civil Affairs statement said. Damage is estimated at $6.2 billion. Floods and landslides in neighboring areas of Myanmar (Burma) have claimed at least 63 lives in the past week.


Figure 2. Paramilitary policemen help evacuate residents from Wanjia village of Fuzhou City, East China's Jiangxi province, June 22, 2010. Days of heavy rain burst the Changkai Dike of Fu River on June 21, threatening the lives of 145,000 local people. Local authorities have ordered immediate evacuation, and the army and paramilitary police have begun conducting rescue operations. Image credit: Xinhua.

Wind and ocean current forecast for the BP oil disaster
Southeast to east winds less than 10 knots will blow in the northern Gulf of Mexico today through Saturday, according to the latest marine forecast from NOAA. The resulting weak ocean currents should cause little motion of the oil slick, according to the latest trajectory forecasts from NOAA and the State of Louisiana. The long range outlook is uncertain, and will depend upon what 93L does.

Resources for the BP oil disaster
My post, What a hurricane would do the Deepwater Horizon oil spill
My post on the Southwest Florida "Forbidden Zone" where surface oil will rarely go
My post on what oil might do to a hurricane
NOAA's interactive mapping tool allows one to overlay wind and ocean current forecasts, oil locations, etc.
Gulf Oil Blog from the UGA Department of Marine Sciences
Oil Spill Academic Task Force
University of South Florida Ocean Circulation Group oil spill forecasts
ROFFS Deepwater Horizon page
Synthetic Aperture Radar (SAR) imagery from the University of Miami

"Hurricane Haven" airing again this afternoon
Tune into another airing of my live Internet radio show, "Hurricane Haven", at 4pm EDT today. Listeners will be able to call in and ask questions. The call in number is 415-983-2634, or you can post a question in the comments area on my blog. You can also email the questions to me today before the show: jmasters@wunderground.com. Be sure to include "Hurricane Haven question" in the subject line. Some topics I'll cover today on the show:

1) The latest on 93L
2) Which model is the most reliable?

Today's show will be 30 - 40 minutes, and you can tune in at http://www.wunderground.com/wxradio/wubroadcast.h tml. The show will be recorded and stored as a podcast.

Jeff Masters

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Quoting 7544:
i dont see anymovement west at this hour looks to be heading nnw imo
You're focusing on the convective band. The movement of this band doesn't represent the actual movement of the system's mid-level circulation. It's actually moving WNW
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Quoting Drakoen:


73.3W is further west than what the Cimss 850mb vort is showing


Meant 72.3, my bad.
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Quoting bappit:


Those high wind speeds look like problems with the algorithm that interprets the data. Don't see how you get 50 knot winds at those angles among all the 10 knot (or less) barbs.


Windsat has "issues" with rain, I would discount those barbs in areas of heavy convection.
Member Since: September 23, 2005 Posts: 14 Comments: 10922
Quoting DestinJeff:


yet even after they are more reliable because they have a llc to initialize on, only those that "fit the narrative" of any particular blogger will be worth anything.



no yournot missing something and the thing is not knowing where its going is the thing that has me the most worried
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Quoting bappit:


Those high wind speeds look like problems with the algorithm that interprets the data. Don't see how you get 50 knot winds at those angles among all the 10 knot (or less) barbs.


It also could be rain contamination or thunderstorm microbursts. The higher wind barbs are shown under some of the stronger convective complexes.
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89. 7544
yeap
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Quoting Grothar:
Anyone know if the Navy site is down?
Link.... Is this the sight you asking about Gro?
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Quoting Patrap:
2km Storm Relative IR Imagery with BD Enhancement Curve

1345 UTC



2km Storm Relative IR Imagery with BD Enhancement Curve

The same infrared imagery shown in the earth relative framework is displayed in a storm relative framework, with a 2km resolution and enhanced with the "BD Curve" which is useful for directly inferring intensity via the Dvorak Enhanced IR (EIR) technique. Scaling is provided by two lightly hatched circles around the center. The two circles have radii of 1 and 2 degrees latitude, respectively.


GIGO
Member Since: May 18, 2006 Posts: 10 Comments: 5961
Quoting 7544:
i dont see anymovement west at this hour looks to be heading nnw imo
I was saying yesterday how I thought it would head over hispaniola... looks to be what is happening.
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2km Storm Relative IR Imagery with BD Enhancement Curve

1345 UTC



2km Storm Relative IR Imagery with BD Enhancement Curve

The same infrared imagery shown in the earth relative framework is displayed in a storm relative framework, with a 2km resolution and enhanced with the "BD Curve" which is useful for directly inferring intensity via the Dvorak Enhanced IR (EIR) technique. Scaling is provided by two lightly hatched circles around the center. The two circles have radii of 1 and 2 degrees latitude, respectively.
Member Since: July 3, 2005 Posts: 421 Comments: 127664
Quoting sammywammybamy:
Can someone pinpoint the center on an image?


On that image "pinpoint" would be a difficult task.
Member Since: May 18, 2006 Posts: 10 Comments: 5961
I'm very sorry about image,bloggers,but i can't find ideal size
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Quoting StormW:


For one thing, yes.


Thanks..I guess the other thing would be the positive 500 HPa height anomaly over the same area...so a northward shift in the jet...but would not the + height anomaly act to supress convection somewhat?
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Quoting hydrus:
It does look really nasty out there.


Those high wind speeds look like problems with the algorithm that interprets the data. Don't see how you get 50 knot winds at those angles among all the 10 knot (or less) barbs.
Member Since: May 18, 2006 Posts: 10 Comments: 5961
The "flag" on a wind barb shows which direction the wind is blowing from and the point shows the direction it's blowing towards. Cool. Thanks.
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morning all
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I think the way and maybe intensity of 93L(Alex) will be:


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I see barbs coming from the West in a couple of areas. This represent surface level winds on Windsat, correct?
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Quoting CyclonicVoyage:



Looking at satellite and comparing to CIMMS 850, seems like the spot to me.


73.3W is further west than what the Cimss 850mb vort is showing
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72. 7544
i dont see anymovement west at this hour looks to be heading nnw imo
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Quoting SavannahStorm:





If that's right we may be cooking with gas...

Quoting muddertracker:

Can you tell from this graphic which direction the winds are blowing? (possible dumb question alert!)


Yes. The "flag" on a wind barb shows which direction the wind is blowing from and the point shows the direction it's blowing towards.
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Anyone know if the Navy site is down?
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Quoting nrtiwlnvragn:
This mornings Navy WindSat solution





Higher resolution Link (you will probably get a certificate warning)
It does look really nasty out there.
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Quoting Drakoen:


NHC is probably justt taking the average of the satellite estimate coordinates along with the tracking of the wave axis.



Looking at satellite and comparing to CIMMS 850, seems like the spot to me.
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Quoting CyclonicVoyage:
15.3N 73.3W heading just N of due west.


NHC is probably justt taking the average of the satellite estimate coordinates along with the tracking of the wave axis.
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Quoting SavannahStorm:




If that's right we may be cooking with gas...

Can you tell from this graphic which direction the winds are blowing? (possible dumb question alert!)
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Quoting StormW:


No ma'am! You got it!!
Good morning Storm. Did you see the GEM today? It has two low pressure areas in the Gulf and a huge blob off the S.E.United States. I was hoping you would check it out and post your thoughts.
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Seems as the day goes on, 93L is slowly starting to gain organization. The two vorts on the 850 mb charts are gone, now just one. Evident of a MLC as Drak pointed out.
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Quoting DestinJeff:


yet even after they are more reliable because they have a llc to initialize on, only those that "fit the narrative" of any particular blogger will be worth anything.


That sounds a bit sarcastic maybe? Just wondering.
Member Since: May 18, 2006 Posts: 10 Comments: 5961
The SAL has come alive in the Atlantic.
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Tropical Update with Oil Gusher LIVE FEEDS
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58. 7544
gfs just might be right on where it ends up
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15.3N 73.3W heading just N of due west.
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Quoting nrtiwlnvragn:
This mornings Navy WindSat solution






If that's right we may be cooking with gas...
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Quoting DestinJeff:


i agree that appearances are that models have an initialization that is further south than what current imagery suggests.

i have begun finding more interest in where models initialize as opposed to where they end.


Good point!
Member Since: May 18, 2006 Posts: 10 Comments: 5961
Quoting smmcdavid:
So what I'm reading, is that we have to wait and see what happens... when and where this thing develops. Then the models will be more reliable. Big shocker.

Am I missing something?
Yes, you are missing all the speculation: insane arguing over where the center is located, track and intensity guesses and name calling.
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Storm W: negative NAO means low shear in the tropical atlantic...is that right?
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Ship in the area of 93L recently reported a WNW wind:



Eagle Anaheim

Last reported at 2010-Jun-22 12:00 UTC. Time now 2010-Jun-22 14:23 UTC.
Position N 15°18', W 074°36'.


Wind from 300 at 19 knots

Waves 1.0 meters (3 feet), 2 second period


Barometer 1012.5 mb
Air temperature 27.0 ° C
Visibility: greater than 5.4 NM
Dewpoint 25.6 ° C
Water temperature 28.0 ° C

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Great Satellite Loop to watch 93L Thanks! Great quality!
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Quoting SomeRandomTexan:
Does anyone have an approx fix on the center


Good question!
Member Since: May 18, 2006 Posts: 10 Comments: 5961
48. 7544
Quoting Jeff9641:
Guys when the COC developes it will be about 100 miles north of the model intialization this morning. Coc should be just south of Haiti and DR in corolation with the mid level circulation.


agree look how it keeps inching further north looks to be going over hati to the bahammas next thats where the conv seems to be building
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Seems like we have a winner in the battle of the COC's.




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Quoting DestinJeff:


yet even after they are more reliable because they have a llc to initialize on, only those that "fit the narrative" of any particular blogger will be worth anything.


True story.

StormW... good to know I'm finally learning. Ha!
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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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