92L still a threat to develop; record SSTs continue in the tropical Atlantic

By: Dr. Jeff Masters , 1:44 PM GMT on September 10, 2010

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A tropical disturbance (92L) over the Lesser Antilles Islands lost most of its heavy thunderstorms last night, due to an infusion of dry air. However, 92L has redeveloped a moderate amount of heavy thunderstorm activity this morning, and remains a threat to the Caribbean--though not as great a threat as it appeared yesterday. Satellite loops show that 92L's heavy thunderstorms are slowly growing in areal coverage, and are becoming more organized. St. Lucia reported sustained winds of 33 mph this morning in a heavy rain squall, and heavy rain showers and gusty winds can be expected throughout the southern Lesser Antilles Islands today. Martinique radar shows that heavy rains are now affecting that island, but there is no rotation to the radar echoes evident. Surface observations indicate that pressures continue to fall at a number of stations in the Lesser Antilles, but no surface circulation is evident in the wind reports. A strong flow of upper level easterly winds is creating a moderate 10 - 20 knots of wind shear on the south side of 92L. The waters are at near-record warmth, 30°C, and these warm waters extend to great depth. Water vapor satellite loops show a large area of dry air lies over the northern Caribbean, and this dry air could interfere with development over the next few days.

Forecast for 92L
The disturbance is moving westward at 5 mph, but steering currents favor a more west-northwest motion Saturday. Lower shear lies over the Central Caribbean, away from the coast of South America, so any northward component of motion will allow for more significant development. There is drier air to the north, but 92L is steadily moistening the atmosphere in the Caribbean, so dry air may not be a problem for it. Model support for development is less than it was yesterday. The GFS and NOGAPS models do not develop 92L. The HWRF, GFDL, and UKMET models predict development, with a track taking 92L into the Dominican Republic on Sunday as Tropical Storm Julia. These models predict the storm will continue west-northwest, affecting Haiti, Eastern Cuba, Jamaica, and the Southeast Bahamas early next week. The ECMWF model foresees a more southerly track, taking 92L into Mexico's Yucatan Peninsula seven days from now.

Residents of the northern Lesser Antilles Islands and Puerto Rico should anticipate the possibility of heavy rains from 92L affecting their islands on Saturday and Sunday, though most of the action will probably stay south and west. The southern Dominican Republic should see heavy rains of 3 - 6 inches on Sunday and Monday from 92L, and Haiti, Jamaica, and eastern Cuba should anticipate similar rains on Monday and Tuesday. Should 92L make a direct hit on the Dominican Republic, it could destroy the storm, though. NHC is giving 92L a 40% chance of developing into a tropical depression by Sunday, which is a reasonable forecast. The first Air Force Hurricane Hunter mission into 92L is scheduled for Saturday morning, but there will be two research missions into the storm today that will give us valuable information on 92L's large scale environment and potential for development.


Figure 1. Morning satellite image of 92L.

Igor
Tropical Depression Igor has survived a bout with high wind shear, and is now in an environment of moderate 10 - 20 knots of shear that should allow for steady strengthening. Waters are warm, 28°C, and the Saharan Air Layer (SAL) is probably not close enough to Igor to prevent development. The models continue to predict development of Igor into a hurricane 2 - 4 days from now. Igor will track west to west-northwest over the next week, with long range forecasts from the GFS and ECMWF models putting the storm several hundred miles northeast of the Lesser Antilles Islands about 6 - 8 days from now. Climatology shows that about 10% of all tropical cyclones that have existed at Igor's current position have gone on to hit the U.S. East Coast; these odds are about 5% for Canada. The forecast steering pattern for the coming two weeks from the GFS model shows a continuation of the pattern we've seen all hurricane season, with regular strong troughs of low pressure moving off the U.S. East Coast. This pattern favors Igor eventually recurving out to sea without affecting any land areas. The odds of Igor hitting land in the U.S. or Canada are probably close to their climatological 10% and 5% probabilities, respectively.

Elsewhere in the tropics
The GFS and ECMWF models predict the development of a new tropical wave off the coast of Africa 3 - 6 days from now.

August SSTs in the tropical Atlantic set a new record
Sea Surface Temperatures (SSTs) in the Atlantic's Main Development Region for hurricanes had their warmest August on record, according to an analysis I did of historical SST data from the UK Hadley Center. SST data goes back to 1850, though there is much missing data before 1910 and during WWI and WWII. SSTs in the Main Development Region (10°N to 20°N and 20°W to 80°W) were 1.23°C above average during August, beating the previous record of 1.01°C set in August 2005. August 2010 was the 7th straight record warm month in the tropical Atlantic. The five warmest months in history for the tropical Atlantic have all occurred this year; June 2005 comes in sixth place, and August 2010 in seventh. As I explained in detail in a post on record February SSTs in the Atlantic, the Arctic Oscillation (AO) and its close cousin, the North Atlantic Oscillation (NAO), are in large part to blame for the record SSTs, though global warming and Atlantic Multidecadal Oscillation (AMO) also play a role.

The Bermuda-Azores High was weaker than average during August, which drove slower than usual trade winds over the tropical Atlantic. These lower trade wind speeds stirred up less cold waters from the depths than usual, and caused less evaporational cooling than usual, allowing August SSTs to remain at record warm levels. The Bermuda-Azores High and its associated trade winds are forecast to be at near-average strength during the next two weeks, according to the latest run of the GFS model. This means that Atlantic SST anomalies will continue to stay at record warm levels during September, significantly increasing the odds of major hurricanes in the Atlantic.


Figure 2. The departure of sea surface temperature (SST) from average for September 9, 2010. Note the area of cool anomalies off the U.S. East Coast, due to the passage of Hurricane Earl. Cool anomalies are also evident east of Bermuda, due to the passage of Hurricane Danielle. Image credit: NOAA/NESDIS.

Next post
I'll have an update Saturday morning.

Jeff Masters

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Quoting StormW:


That's correct.

That's why you can see the trof coming off the east coast.



but this is not what you expect to continue?
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btw..

when a storm system looks "weak" during the day, I've noticed that if it has a spin, and it has a lot of moisture around, and the area around it can get heated up for sun down, DMAX has a huge effect on it
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When it gets into octant 1 and 2, we should see development occur closer to 55W and westward.

Landfall will depend on the ridge setup.

Storm, when is the MJO forcast to be in 1 & 2?
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I don't think that was what he was saying about Igor.....

Quoting Caribbeanislands101:
it makes sense, we should see igor turn west and could even deep a little south of west
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Good morning all.

Tropical Tidbit for Friday, September 10th, with Video
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Quoting StormW:



No...the high is still going to build, hence the almost due west course..the shortwaves will aid the trof in eroding the western portion.
it makes sense, we should see igor turn west and could even deep a little south of west
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Sorry Storm! (pouts and realizes he is right)...

Quoting StormW:
Said it before, and I'll say it again...If ignorance is bliss, then Doctor Masters blog is in ecstasy.
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Quoting StormW:
Ok...hopefully this will explain some things. There will still be some that will refuse to believe what I'm saying, although it's in black and white (or in this case, "color")...but here goes

The following is the MJO daily index graph. When the MJO is in the Octants with the plus marks, the atmosphere is in the condition for us to see the trof that is causing all the re-curves, to be in the position it's in.

When the MJO is in the Octants with the dash lines...this is when we say bye bye to that trof...and things change as far as cyclone tracks (Alex, Bonnie, etc.)...except in this case, the change will take place when we still have CV systems to deal with.



Here is the forecast for the MJO...where is it headed?




Another indication is the NAO trend, which indicates a change, albeit brief, to the A/B High.



That's how we get to a pattern that looks like this:



Hence, my current blog forecast.


ok. so i am confused. i see sept. 9 in octant 4, one with the plus marks, so trough recurving still in place??
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I'll agree that on satellite there is quite a good spin at the surface....

Quoting leo305:
92L is looking amazing.. at the surface.. and it has a lot of moisture to work with
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342. IKE
I went back and checked....back to 1990...the last 20 years of the Atlantic tropical season......

Since 1990...from September 16th of each year on, the number of named systems that have formed(at least as a tropical storm), BEFORE 40W, that made lower 48 landfall......zero.
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92L is looking amazing.. at the surface.. and it has a lot of moisture to work with
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Igor's more modest now:

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Quoting KEEPEROFTHEGATE:


what is that?
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Quoting StormW:
Ok...hopefully this will explain some things. There will still be some that will refuse to believe what I'm saying, although it's in black and white (or in this case, "color")...but here goes

The following is the MJO daily index graph. When the MJO is in the Octants with the plus marks, the atmosphere is in the condition for us to see the trof that is causing all the re-curves, to be in the position it's in.

When the MJO is in the Octants with the dash lines...this is when we say bye bye to that trof...and things change as far as cyclone tracks (Alex, Bonnie, etc.)...except in this case, the change will take place when we still have CV systems to deal with.



Here is the forecast for the MJO...where is it headed?




Another indication is the NAO trend, which indicates a change, albeit brief, to the A/B High.



That's how we get to a pattern that looks like this:



Hence, my current blog forecast.


Dang
Member Since: August 23, 2008 Posts: 0 Comments: 1918
hee hee, keep telling yourself that.....don't write anything off until it is DONE.

Quoting help4u:
Yesterday dangerous storm 92l ,gloom and today ,today everything coming up roses!So it is in the world of weather!
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Yesterday dangerous storm 92l ,gloom and today ,today everything coming up roses!So it is in the world of weather!
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Yeah, he is just not looking at a good visible image - not likely looking at the vort max map either...

Quoting btwntx08:

???
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thanks for posting these pics storm. so, if I understand you correctly, we are in an MJO phase which promotes tropical development.

With that said, am I reading this correctly in that the numbers bolded (24, 25, etc..) are above the dashed line.

So, this means as we get late into September and October, this favors more landfalls?

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I am thinking tonight, at Dmax we might see a little more "activity" out of 92L......today seems like another "building the house" so to speak, day.

Quoting wayfaringstranger:


True but it has positioned itself further away from South America...maybe later in the day we would see more moisture and intensity
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324. JRRP
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Quoting Goldenblack:
It is still very broad and needs some sustained convection.


True but it has positioned itself further away from South America...maybe later in the day we would see more moisture and intensity
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It is still very broad and needs some sustained convection.

Quoting wayfaringstranger:


That looks like what could be a depression...
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Quoting JRRP:


That looks like what could be a depression...
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Look at the visible satellite, you will see spin:

Visible Satellite Loop


Quoting weathermanwannabe:
Afternoon....Igor looking good but 92L going nowhere at the moment......No spin at all that I can discern and convection has been waning all morning....I can see why some of the models do not develop it as mentioned by Dr. M above.
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318. JRRP
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Afternoon....Igor looking good but 92L going nowhere at the moment......No spin at all that I can discern and convection has been waning all morning....I can see why some of the models do not develop it as mentioned by Dr. M above.
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92l isn't going to do much. Igor is for the fish.:)
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Quoting tampahurricane:
I have a question now with 92L if this thing gains strength and finds its way into the Gulf of Mexico could there be a Hurricane Charley type scenario with all these trof's of low pressure moving off the coast, recurving the storm into the west coast of Florida? just a question not wish casting. Thanks


Not likely, it could, but current steering layers and the building back of that ridge brings the track more southerly towards the Yucatan.
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Quoting tampahurricane:
I have a question now with 92L if this thing gains strength and finds its way into the Gulf of Mexico could there be a Hurricane Charley type scenario with all these trof's of low pressure moving off the coast, recurving the storm into the west coast of Florida? just a question not wish casting. Thanks


I wouldn't board up the windows, but I wouldn't take my eye off it either. Too early.
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I have a question now with 92L if this thing gains strength and finds its way into the Gulf of Mexico could there be a Hurricane Charley type scenario with all these trof's of low pressure moving off the coast, recurving the storm into the west coast of Florida? just a question not wish casting. Thanks
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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.