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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Wouldn't it be funny if Avila was reading the blog and saying, "Hey guys, lets not post it 'till 11:20' .....hehehhe
Member Since: September 25, 2007 Posts: 53 Comments: 8533
Quoting sammywammybamy:
Florida going to get Wet tommorow by a Tropical Wave


Doe I hope that doe not develop in the gulf.
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Quoting sammywammybamy:
WHEN IT COMES OUT I WILL PUT IT IN BOLD


Oh we know lol
Member Since: June 9, 2007 Posts: 4 Comments: 15950
Quoting Stormchaser2007:
Sammy focus here...

The lives of a few suicidal blogger hang in the balance.



LMAO!
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting TampaSpin:
Ok SAmmy you are in charge of post the NHC update.....this is a very large task......DON'T let us down......LMAO
lmao!!
Ike... too funny lmao!
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Quoting viman:


Hey W456, how are things in SKB, keeping an eye out for this potential double whammy.


I thought 90L was the only threat but then reconsidered TD 2.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
LOL!!!!
Member Since: September 25, 2007 Posts: 53 Comments: 8533
Sammy focus here...

The lives of a few suicidal blogger hang in the balance.
Member Since: June 9, 2007 Posts: 4 Comments: 15950
Ok SAmmy you are in charge of post the NHC update.....this is a very large task......DON'T let us down......LMAO
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting KoritheMan:


The upper-level wind forecast looks to be a favorable one for tropical cyclogenesis over the next several days. The tropical wave near Cuba could move into the Gulf in two days or so, and help to enhance thunderstorm activity there by interacting with the current trough in the NE Gulf. Something to watch, to be sure.

Thank you for the response, there is no doubt about that. The Gulf water is really hot.
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oh the suspense!!!
LOL
2919. Patrap



40,000 Blogger's online awaiting the 11pm..

C'mon,C'mon....!!!!
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Quoting BajaALemt:
ROFL Tim!! I dont think I've EVER seen just ONE person post the TWO


Its WU tradition that we post more than 1.
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Quoting atmoaggie:

Honestly, I know where to get it, I plan on doing so, I don't need it posted here at all. I would prefer that, actually.


good point
Member Since: July 24, 2005 Posts: 407 Comments: 19076
2916. viman
Quoting Weather456:
somestimes if you refresh the NHC page too long it causes delay in posting the updates. just slow down on the F5 key


Hey W456, how are things in SKB, keeping an eye out for this potential double whammy.
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ROFL Tim!! I dont think I've EVER seen just ONE person post the TWO
Member Since: September 25, 2007 Posts: 53 Comments: 8533
2913. IKE
Quoting Weather456:
what if the NHC page says nothing by 11PM


A few in here will hang themselves...jump off bridges....
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I agree on sammy doing it..
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Quoting Stormchaser2007:


A few will cry...

Some may never recover.


lol lol lol
Member Since: July 24, 2005 Posts: 407 Comments: 19076
OK

I plotted the positions of exTD2 from 5pm yest to where it is now and it looks like about 490 miles in 30 hours for a fwd speed of 16.3 mph...

That's close enough for me.

CRS
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2853. CaicosRetiredSailor

Latest tropical weather discussion:

THE REMNANT 1010 MB LOW PRESSURE CENTER OF TROPICAL DEPRESSION
TWO IS NEAR 15N43W...MOVING WESTWARD ABOUT 10 KT.

Of course a new outlook should come out shortly
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Quoting TampaSpin:
I vote we let SAMMYWammyBammy post it....
agreed
2905. hahaguy
Quoting TampaSpin:
I vote we let SAMMYWammyBammy post it....


Sounds good lol.
Member Since: August 12, 2007 Posts: 2 Comments: 2838
Quoting TampaSpin:
Ok.....lets decide who wants to post it...and please nobody else......

Honestly, I know where to get it, I plan on doing so, I don't need it posted here at all. I would prefer that, actually.

Addendum: There is that other shoe.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Parkersburg tornado was at one point over a mile wide - no house was in its path for more than 60 seconds...
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Quoting CycloneOz:


faster...Faster...FASTER!!!!!


>_>

X rated much?
Member Since: March 7, 2007 Posts: 602 Comments: 21333
Quoting Weather456:
what if the NHC page says nothing by 11PM
we will all die, of cardiac arrest! LOL
I vote we let SAMMYWammyBammy post it....
Member Since: September 2, 2007 Posts: 179 Comments: 20448
Quoting Weather456:
what if the NHC page says nothing by 11PM


A few will cry...

Some may never recover.
Member Since: June 9, 2007 Posts: 4 Comments: 15950
2898. Patrap
90L 1800 UTC

Multiplatform Satellite Surface Wind Analysis




90L 0000 UTC




Multi-Platform Tropical Cyclone Surface Wind Analysis

This product combines information from five data sources to create a mid-level (near 700 hPa) wind analysis using a variational approach described in Knaff and DeMaria (2006). The resulting mid-level winds are then adjusted to the surface applying a very simple single column approach. Over the ocean an adjustment factor is applied, which is a function of radius from the center ranging from 0.9 to 0.7, and the winds are turned 20 degrees toward low pressure. Over land, the oceanic winds are reduced by an additional 20% and turned an additional 20 degrees toward low pressure.

The six datasets used are the QuikSCAT scatterometer, which is adjusted upward to 700 hPa in the same manner as the surface winds are adjusted downward, ASCAT scatterometer (treated the same way as QuikSCAT), feature track winds in the mid-levels from the operational satellite centers, 2-d flight-level winds estimated from infrared imagery (see Mueller et al 2006 ) and 2-d winds created from Advanced Microwave Sounding Unit (AMSU)- derived height fields and solving the non-linear balance equations as described in Bessho et al (2006).

Each of the input data are show in subpannels following the analysis (i.e., storm-relative). Shown are AMSU winds, Cloud-drift/IR/WV winds, IR-proxy winds and Scatterometer winds; QuikSCAT (BLUE) and ASCAT (RED). All input data in these panels has been reduced to a 10-m land or oceanic exposure depending on the location (i.e., non-surface data has been reduced to a 10-m exposure)
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Quoting Relix:
I am still not believing this will hit PR. Can't find a way for it to.... or am I being toooo optimistic? =(


If you are talking about 90L, then a PR strike is a possibility, but I think it's likely it will pass a bit north of there.
Member Since: March 7, 2007 Posts: 602 Comments: 21333
Quoting Weather456:
what if the NHC page says nothing by 11PM


I would LOL. Than cry.
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Quoting TampaSpin:
Ok.....lets decide who wants to post it...and please nobody else......
im posting
OMG I didn't know about the F5 button! I so dumb! LOL
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Quoting KerryInNOLA:


Hey Kerry!
Member Since: March 19, 2009 Posts: 0 Comments: 1421
what if the NHC page says nothing by 11PM
Member Since: July 24, 2005 Posts: 407 Comments: 19076
Quoting Ameister12:
Ahh!!!
How much longer can I wait for these flipping storms to become TDs!!!

Forever would be OK. I would need to find another niche in my field, though.
Member Since: August 16, 2007 Posts: 6 Comments: 12463
Quoting mossyhead:

i can see 100 repeats of the post. that is aggravating.

lets have a contest. who can guess how may repeats of the posting of the 11pm advisory?
Member Since: July 7, 2008 Posts: 0 Comments: 473
Quoting DestinJeff:


F5 buttons everywhere are being rubbed raw
lmao!
Ok.....lets decide who wants to post it...and please nobody else......
Member Since: September 2, 2007 Posts: 179 Comments: 20448
2885. Relix
I am still not believing this will hit PR. Can't find a way for it to.... or am I being toooo optimistic? =(
Member Since: Posts: Comments:

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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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