Disturbance 90L close to tropical depression strength; TD 2 may rise again

By: Dr. Jeff Masters , 2:02 PM GMT on August 14, 2009

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A strong tropical wave (90L), with a large circulation and a moderate amount of heavy thunderstorm activity, is a few hundred miles southwest of the Cape Verdes Islands, off the coast of Africa. This morning's QuikSCAT pass shows that 90L has a large circulation, but this circulation is not yet well-formed, as it is elongated along an east-west axis. Satellite imagery from the European METEOSAT satellite show that the heavy thunderstorms associated with 90L are gradually becoming better organized, with some spiral banding evident on the south side of the storm. Satellite intensity estimates from NOAA already put 90L at tropical depression strength with 30 mph winds, but the storm does not yet have a well enough formed circulation to be classified as a depression. Water vapor imagery shows that since 90L is forming several hundred miles south of the dry air of the Saharan Air Layer (SAL), the storm should not be affected by dry air and dust as much as Tropical Depression Two was. However, there is some dry air from the SAL being sucked into the circulation of 90L, and this is retarding its development.

Wind shear is moderate, about 10 - 15 knots, but is forecast to fall to the low range, 5 - 10 knots, later today. Shear is then forecast to remain low for the next five days. Sea Surface Temperatures are about 28°C, and will remain in the 27 - 28°C range the next five days. The combination of low wind shear and sufficiently warm SSTs should allow 90L to develop into a tropical depression by Saturday, and potentially reach hurricane strength by Wednesday. Most of our reliable models strengthen 90L into a hurricane by Wednesday, when the storm is expected to be near the northern Lesser Antilles Islands. One important outlier is the ECMWF model, which has 90L passing to the north of the islands, and eventually recurving out to sea east of Bermuda. The ECMWF was by far the most reliable model for forecasting hurricane tracks last year. However, all of our models are pretty unreliable going out 5 days in advance for systems that have yet to reach tropical depression strength. Once 90L becomes a tropical depression and develops a well-formed circulation, the models will have a better handle on forecasting where it will go.


Figure 1. The remnants of Tropical Depression Two (left side of image) and tropical wave 90L (right side of image).

Tropical Depression Two may come back
Tropical Depression Two died yesterday, but may rise again. Satellite loops of the remnants of the storm show that heavy thunderstorms are again attempting a comeback near the axis of what is now a tropical wave. However, dry air continues to interfere with the development of the thunderstorm activity, and moderately high wind shear of 15 - 20 knots is also inhibiting the process. Wind shear over the remnants of TD 2 is expected to remain in the moderate range, 10 - 20 knots, over the next four days. Sea Surface Temperatures (SSTs) are 27°C, but will warm to 28°C two days from now. There is plenty of dry, stable air from the Saharan Air Layer (SAL) to the north and west that will continue to cause the storm problems. The relatively cool SSTs and dry air mean that any re-development of the storm will be slow to occur. NHC has given the system a medium (30 - 50% chance) of becoming a tropical depression again by Sunday morning. Only one reliable model, the NOGAPS, is predicting regeneration of TD 2. The NOAA Hurricane Hunters are flying research missions into the remnants of TD 2 today and Saturday.

I'll have an update Saturday morning, or earlier, if significant developments occur.

Jeff Masters

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Continues to show new cyclone

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Quoting nrtiwlnvragn:
The NOAA jet reported its first dropsonde data. You can view it at Tropical Atlantic by selecting Dropsonde Report (UZNT13) under Main NOAA Products (KWBC): on the right hand side of the page. Paste the data into the decoder.

we should be looking at what level
1011mb
1000mb
925mb
850mb
700mb
500mb
400mb
300mb
250mb
200mb
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Why does this blog become so hateful. This is not a highschool clique. It is a place to learn and take part in a profession, hobby, past time...why ever you are here. Either way, no one would be here if we weren't genuinely interested in the tropics. Cut some slack!
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Quoting Patrap:
Just a little favor to ask people... Do you think you could refrain from quoting the pesky trolls? I know you are saying something in response to their ill informed posts, but I would be so much happier (and I think others would too) if you would just use their post number and/or name and respond rather than making everyone see their post again. I particularly have stormno on my ignore list but have been forced to read his posts about 6 times this evening. Thanks so much! Off the soap box now.

Thanks for mentioning that as for those who do ignore the irresponsible ones,..it kinda makes the feature were using moot.
In others words,please dont quote idiocy,just use the Post # if you must respond


Thanks Pat! Well said.
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Is it legal to yell "pinhole eye" in a crowded blog?
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That's alright big fat guy its still a sexy name.
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Quoting Grothar:

Good question. I live in Ft. Lauderdale on the beach so a little concern here as well. Also can anyone on the blog explain the elongation in both features. What are the atmospheric conditions which causes it, and when would one expect a more concentric form?


Hey there don't worry or quote WS. He is just following the lead.Follow the comments from the people actually putting up info, they usually have there own blogs and synops.
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Speak of the devil I was thinking of skyponey also.I believe she was right on the money with her statement that we are lucky Cuba's mountains and wind shear is messing with the wave in the fl straits. I wonder if it will move a little farther west then models show. If so not a good scenario for the gulf.
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Well then you need to move to Bill, Georgia Girlfriend

Quoting SavannahStorm:
WS, as much as you might wish it, I'm a dude. A fat, ugly dude.

BTW, you're not the first to make that mistake. I live in Savannah. My name is not Savannah.
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1674. JLPR
Quoting WeatherStudent:


Yes, has she said anything the situation? trust her, Solemnly, and not the fools at AccuWeather for the love of God.


yep that's very irresponsible of them
they are forecasting TS winds while no storm has formed yet =\
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Quoting Weather456:
look how far west the models shift



The XtremeHurricanes.com team has been waiting for the models to move this system further west.

Our current plans are to establish our first base near the LA Gulf Coast mid-way through next week.

Once forecasters are more clear on the storm's track, we'll begin the live webcam countdown to go-live and move into position to intercept the storm. If the storm veers out to sea, our potential coverage of the storm will end.

Disclaimer: XtremeHurricanes.com is staffed with professional hurricane chasers who have years of experience within dangerous tropical cyclone systems. Our purpose as journalists is to cover U.S. landfalling hurricanes. We insist that if you are affected by a landfalling hurricane that you do not venture outside to "experience" the hurricane. If you have not evacuated prior to the storm affecting your community, protect yourself as best as possible inside a shelter until the storm abates.
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WS, as much as you might wish it, I'm a dude. A fat, ugly dude.

BTW, you're not the first to make that mistake. I live in Savannah. My name is not Savannah.
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1668. Grothar
Quoting WeatherStudent:


It's beyond jumping then gun, ma'am.

Good question. I live in Ft. Lauderdale on the beach so a little concern here as well. Also can anyone on the blog explain the elongation in both features. What are the atmospheric conditions which causes it, and when would one expect a more concentric form?
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02L definitely seems to be having some decent outflow in all quadrants whereas earlier today it was limited to I,II, and III.
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Quoting Vortex95:


456 if you feel that you can answer this, when you thik 90l will develop?

Also people in your area looking at this?


I gave 90L a time frame between Friday and Sunday, and it seems resonable. It is slow no organize, no surprise there, since it is large.


Also, I mentioned it on the blog yesterday that the met officies and hurricane correspondents all across the Eastern Caribbean are monitoring this feature and only 2 storms I here everyone mentioning, Hugo and Georges. Marilyn 1995 comes to mind, thats what the ECMWF is showing.

Though this far out I havnt raise the concern much. As we enter next we should have a better idea. Though 90L is only 5-6 days away. To show how close that is, 99L developed about 5 days ago. Time can fly.
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The NOAA jet reported its first dropsonde data. You can view it at Tropical Atlantic by selecting Dropsonde Report (UZNT13) under Main NOAA Products (KWBC): on the right hand side of the page. Paste the data into the decoder..

They are updating automatically now, just select the green updated data.
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Interesting.. GFS very bullish on wave behind 90L

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1662. Patrap
Just a little favor to ask people... Do you think you could refrain from quoting the pesky trolls? I know you are saying something in response to their ill informed posts, but I would be so much happier (and I think others would too) if you would just use their post number and/or name and respond rather than making everyone see their post again. I particularly have stormno on my ignore list but have been forced to read his posts about 6 times this evening. Thanks so much! Off the soap box now.

Thanks for mentioning that as for those who do ignore the irresponsible ones,..it kinda makes the feature were using moot.
In others words,please dont quote idiocy,just use the Post # if you must respond
Member Since: July 3, 2005 Posts: 424 Comments: 128290
1661. JLPR
Quoting WeatherStudent:


And you believe them? Stick to that main female, Chief Meteorologist from your local Univision news station down there. She's the main lead when it comes to Tracking the Tropics over there in La Isla del Encanto, OK? I can't recall her name, by the way. :)


That would be Ada Monzon
yep she is good with the weather xD
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I doubt AccuWeather.com goes to every single city in the world and creates a forecast based upon "hype". They are probably generated by the computer models which show a Tropical Storm hitting Puerto Rico in a week.
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1658. jipmg
Quoting RainyEyes:
How are they forecasting hurricane force winds 5 days in advance before it has even been named and before the models can be close to accurate due to change in forward speed winds etc. I am definitely an ameature, but isn't that jumping the gun?


Its actually tropical storm force, its Kilometers per hour not knots
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Agreed Kman. Agreed. Oh well time to pack it up from the second floor office building on US 19. In Clearwater.
Member Since: Posts: Comments:
Just a little favor to ask people... Do you think you could refrain from quoting the pesky trolls? I know you are saying something in response to their ill informed posts, but I would be so much happier (and I think others would too) if you would just use their post number and/or name and respond rather than making everyone see their post again. I particularly have stormno on my ignore list but have been forced to read his posts about 6 times this evening. Thanks so much! Off the soap box now.

So about those storms... I'm wish nobody any harm, but I am excited to have something to watch in the tropics. It makes working with the National Weather Service much more exciting! But hopefully we aren't threatened too closely- nobody wants 12 hour shifts!
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Quoting Weather456:
look how far west the models shift

I see that ...and the one sticking out over the NW tip of Cuba makes me veeeerrrrryyy nervous....
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Quoting SavannahStorm:


Ahem, who you callin girl?

LOL. Don't mind me as I almost choke on my water trying not to laugh out loud in my office.
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How are they forecasting hurricane force winds 5 days in advance before it has even been named and before the models can be close to accurate due to change in forward speed winds etc. I am definitely an ameature, but isn't that jumping the gun?
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Quoting Patrap:
NOAA’s “Hurricane Hunter” Aircraft
Lockheed WP- 3D Orions (P- 3s) and Gulfstream IV SP (G- IV) Jet

G-IV Jet—Seeking the Storm's Path
Since the beginning of the 1997 hurricane season, the G-IV has flown missions around every Atlantic-based hurricane that has posed a potential threat to the United States. The jet's mission covers thousands of square miles surrounding the hurricane, gathering, with newly developed GPS dropwindsondes, vital high-altitude data needed for improved numerical forecast models. The G-IV has added a vital new dimension as it maps the steering currents that influence the movement of hurricanes.

Data from GPS dropwindsondes that measure pressure, temperature, humidity, and wind information are relayed to the aircraft for transmission by satellite to the National Hurricane Center in Miami and the National Centers for Environmental Prediction in Camp Springs, Md. There the data are available for many numerical forecast models, providing important information about regions—mostly over oceans—in which there are no other sources of weather data.

G-IV flight data are expected to help numerical guidance computer models improve hurricane landfall and track forecasts by up to 20 percent, and to further refine storm intensity forecasts.

After hurricane season, NOAA's interest in severe weather becomes focused on the winter storms affecting the western, central and northeastern United States. NOAA has used the G-IV to help monitor and study these storms to advance our understanding of them and improve winter storm forecasts. The G-IV has also been used to study clear air turbulence—a condition that threatens the safety of air traffic—over the Pacific Ocean, helping scientists increase their ability to understand and predict this potentially deadly phenomenon.


Thanks for the link!
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1649. jipmg
Wait there's a hurricane hunter plane going towards ex TD 2 right now? I had no idea
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look how far west the models shift

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Quoting Patrap:
Patrap..do you know how many (if any) dropsondes the NOAA G IV will launch?


Im not 100%b sure that they even use dropsondes the G-4,thet
y usually use other instruments to sample the upper air environment around the Systems Periphery.

Maybe someone Like Skyepony would have a better answer for you


OK, Thanks. I have heard they do; I believe they have a wind lidar and doppler radar but can deploy dropsones; the "full trop" variety.
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1644. Patrap
NOAA’s “Hurricane Hunter” Aircraft
Lockheed WP- 3D Orions (P- 3s) and Gulfstream IV SP (G- IV) Jet


G-IV Jet—Seeking the Storm's Path
Since the beginning of the 1997 hurricane season, the G-IV has flown missions around every Atlantic-based hurricane that has posed a potential threat to the United States. The jet's mission covers thousands of square miles surrounding the hurricane, gathering, with newly developed GPS dropwindsondes, vital high-altitude data needed for improved numerical forecast models. The G-IV has added a vital new dimension as it maps the steering currents that influence the movement of hurricanes.

Data from GPS dropwindsondes that measure pressure, temperature, humidity, and wind information are relayed to the aircraft for transmission by satellite to the National Hurricane Center in Miami and the National Centers for Environmental Prediction in Camp Springs, Md. There the data are available for many numerical forecast models, providing important information about regions—mostly over oceans—in which there are no other sources of weather data.

G-IV flight data are expected to help numerical guidance computer models improve hurricane landfall and track forecasts by up to 20 percent, and to further refine storm intensity forecasts.

After hurricane season, NOAA's interest in severe weather becomes focused on the winter storms affecting the western, central and northeastern United States. NOAA has used the G-IV to help monitor and study these storms to advance our understanding of them and improve winter storm forecasts. The G-IV has also been used to study clear air turbulence—a condition that threatens the safety of air traffic—over the Pacific Ocean, helping scientists increase their ability to understand and predict this potentially deadly phenomenon.
Member Since: July 3, 2005 Posts: 424 Comments: 128290
Quoting NOSinger:
Does anyone have a link for the CMC and the GFDL?

Main page of this blog has all the models on it.!
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Quoting SavannahStorm:


Ahem, who you callin girl?


LOL..
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Does anyone have a link for the CMC and the GFDL?
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Caribbean forecasts are based on models derived conditions. So 90L will be close enough to the Northeast Caribbean to produce tropical storm forced winds. However, local forecasts defer from forecast made by the Weather Channel and Accuweather becuz we incoporate much more than just models. remember accuweather and the weather channel dont monitor international weather.
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Quoting jipmg:


oh I thought I had read 80 knots, its actually 80 kilometers


Acuweather, the Enron of forecasting...
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Quoting WeatherStudent:


That's old, girl.


Ahem, who you callin girl?
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1637. Patrap
Patrap..do you know how many (if any) dropsondes the NOAA G IV will launch?


Im not 100%b sure that they even use dropsondes the G-4,thet
y usually use other instruments to sample the upper air environment around the Systems Periphery.

Maybe someone Like Skyepony would have a better answer for you
Member Since: July 3, 2005 Posts: 424 Comments: 128290
THEN WHAT DRAK?
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1634. jipmg
Quoting JLPR:


huh?

Very windy; overcast with a couple of thunderstorms around. Winds from the SE at 44 mph.


oh I thought I had read 80 knots, its actually 80 kilometers
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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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