Two waves to watch

By: Dr. Jeff Masters , 2:06 PM GMT on July 29, 2006

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The tropical wave near 9N, 46W, about 1000 miles east of the southernmost Lesser Antilles Islands, continues to show signs that it may organize into a tropical depression. While we don't have a good recent QuikSCAT pass to look at, this morning's visible satellite imagery shows a pronounced surface circulation. However, the amount of heavy thunderstorm activity has greatly decreased since yesterday, due to the ingestion of dry Saharan air from the north (Figure 1). Dry air will continue to be a problem for the wave the farther north it goes. The forecast tracks from the latest computer models (Figure 2) show a mostly westward track, but the wave is expected to slowly gain latitude, putting it more into the influence of this very dry air from Africa.


Figure 1. Saharan air layer (SAL) analysis from 8am EDT Sat Jul 29. Dry, dust laden air from the Sahara desert is coded orange, and lies just north of the tropical wave we're tracking. Image credit: University of Wisconsin CIMSS and NOAA's Hurricane Research Division.

In the wave's favor, it is under only 5-10 knots of wind shear, and this shear is forecast to remain weak over the next two days. As the wave approaches the Lesser Antilles Islands on Monday, shear is forecast to increase again. Sea surface temperatures are favorable--28 C, about 2 degrees C above the threshold of 26 C needed for tropical storm formation.

The long term outlook for the system is not favorable, due to the large amount of dry air to its north and the increasing wind shear likely to affect the system once it nears the islands. In addition, the wave is expected to cross into the southeast Caribbean. This region is climatologically unfavorable for tropical cyclones, because the land mass of South America cuts off the inflow of moist air from the south, replacing it with drier continental air.

None of the computer models develop this wave into a tropical storm.


Figure 2. Preliminary model tracks for the tropical wave approaching the Lesser Antilles Islands.

Tropical wave south of Puerto Rico
An area of heavy thunderstorms associated with a westward-moving tropical wave has increased in coverage just south of Puerto Rico and the Dominican Republic this morning. Wind shear over this disturbance is marginal for development, 10-20 knots, so some slow development is possible over the next few days. This disturbance probably has more potential than the other wave, due to the presence of much moister air in the Caribbean.

Jeff Masters

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832. MZT
2:26 PM GMT on July 30, 2006
I'd put 99L at about 12N 52.5W, and we've been saying the warm water begins around 55W. I think if 99L has gotten this far and has retained circulation for this long, TD formation is fairly likely.

It's still pretty exposed on the west side, but 99L keeps on working at it.

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831. Cavin Rawlins
1:51 PM GMT on July 30, 2006
new blog is up......
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830. aquak9
1:47 PM GMT on July 30, 2006
new thread, ya'll....
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829. SLU
1:47 PM GMT on July 30, 2006
as long as the convection continues to explode then the winds will follow suit
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828. SLU
1:45 PM GMT on July 30, 2006
Thats true 456. 99L has 3/4 of a circulation now .... we need to get the westerlies blowing on the southern side and we're good to go. Having said that, the circulation is better define now than it was in last evenings QUIKSCAT pass
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827. Skyepony (Mod)
1:42 PM GMT on July 30, 2006
At times the last system we watched in the gulf was showing more circulatation than that. 99L has a good kink to it, yes the circulation looks slightly better then it did yesterday, but where has it's winds gone? I remain unimpressed with 1 red vector.
Member Since: August 10, 2005 Posts: 162 Comments: 37829
826. dylan3112
1:36 PM GMT on July 30, 2006
The cmc and the gfs both develop a storm coming off the african coast in about 4 to 6 days but the gfs develops it before the cmc, and also the gfdl shows the high breaking down just enough to turn 99L north right by flordia but the rest of the models show it not breaking down enough to turn it up the east coast
824. Cavin Rawlins
1:35 PM GMT on July 30, 2006
Skyepony, if that quick sat map is right i would say that 99L has a circulation but its not closed. That is not unimpressive. If that was to closed today there will bo doubt that TD 03 will form.
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823. Skyepony (Mod)
1:35 PM GMT on July 30, 2006
Now the PR wave is getting some wind to it.
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822. Tazmanian
1:34 PM GMT on July 30, 2006
...Tropical waves...
A Caribbean Sea tropical wave is along 72w/73w south of 20n
moving west 20 kt. Numerous strong showers and thunderstorms
have shifted and now cover the British Virgin Islands and the
U.S. Virgin Islands from 17n to 20n between 64w and 67w.
Lingering precipitation over Puerto Rico still is possible. All
the coldest cloud top temperatures now are over the waters to
the east and north of Puerto Rico. Shower and thunderstorm
activity associated with a tropical wave has become a little
better organized this morning. Some slow development of the
system is possible during the next few days
Member Since: May 21, 2006 Posts: 5091 Comments: 115085
821. Cavin Rawlins
1:32 PM GMT on July 30, 2006
SLU, your're right... the PR has more tightly organize showers than 99L
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820. Skyepony (Mod)
1:30 PM GMT on July 30, 2006
The latest QuikSCAT of 99L is pretty unimpressive.
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818. SLU
1:27 PM GMT on July 30, 2006
While all the attention is fixed on 99L (and quite rightly so) the PR wave is actually looking in good shape and the San Juan radar is showing a tight swirl just NNW of San Juan. Plus surface observations there show light and variable winds in the last few hours which is one indication of a circulation trying to form to the north.
Member Since: July 13, 2006 Posts: 12 Comments: 5132
817. code1
1:25 PM GMT on July 30, 2006
Welcome back 12. We are seeing more and more of our old friends coming back now. Good to see. We also have a lot of new friends this year. WU is growing fast!!
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816. Cavin Rawlins
1:24 PM GMT on July 30, 2006
Well, I must admit that 99L is hanging on pretty long....and now this morning looks more organize.
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814. Cavin Rawlins
1:09 PM GMT on July 30, 2006
so Rand.....the GFDL is a more accurate model?
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813. Cavin Rawlins
1:07 PM GMT on July 30, 2006
The Puerto Rican wave has become a little better organized this morning. No dust to deal with but high wind shear to its north, but that not may be for long, as It looks like its weakening.

Member Since: July 24, 2005 Posts: 407 Comments: 19076
812. miamihurricane12
1:05 PM GMT on July 30, 2006
morning everybody, this is my frist post since last season...but in regards to the models, the GFDL is better with deeper or stronger system and in this case developed systems, the model which should be looked at right now is the BAMM models b/c they are shallower models better for undeveloped systems but honestly their is not any good models for predicting undeveloped systems. My guess is that 99L will not develop until it gets closer to the lesser antilles and gains some more lattitude and in which case it may encounter more shear and dry air...so my best guess is to watch the system over PR and and Virgin islands right now

Great to be back everybody
810. Cavin Rawlins
1:02 PM GMT on July 30, 2006
Does any of the models develop this to be a TD, TS or H....?
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809. Cavin Rawlins
1:00 PM GMT on July 30, 2006
Good Morning All...

Sunday July 30th 9:00am EDT

99L became a little better organized overnight...also it moved north, now located at 11N......


Shear- The system currently has little shear to deal with but increasing towards the islands....

Dust- Heavy dry air to the north and west but on water vapor imagery seems to be not affescting 99L

Intensity- 99L is now 30mph, with a central pressure of 1008mbar.

Chances-Well it is almost a depression. But due to increasing marginally to hostile conditions, and lack of convection, it remains 15%.
Member Since: July 24, 2005 Posts: 407 Comments: 19076
808. icepilot
12:59 PM GMT on July 30, 2006
You're wecome SJ

Looks like 99 will take a day to decide what it will do - I agree prob go N
see you all tomorrow.
Member Since: July 9, 2005 Posts: 0 Comments: 387
806. GainesvilleGator
12:53 PM GMT on July 30, 2006
Well, the good news is that if the two tropical waves we are watching continue sliding north, crude speculators will have to wait another week for a system to enter the Gulf of Mexico.

My sister is trying to sell her house in Wellington (Palm Beach County). I think it has 4 bedrooms & 3 baths. Anyone looking for a house in this area?
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805. StormJunkie
12:53 PM GMT on July 30, 2006
Thanks ice, and good to see you. I bet that was a very interesitng job :)
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804. icepilot
12:52 PM GMT on July 30, 2006
And for what it's worth - I've watched the GFDL for several years - I've come to weight it more than the others when evaluating their outputs
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803. StormJunkie
12:51 PM GMT on July 30, 2006
I can understand that Rand, I don't know a lot about it's record on invests. Was too busy watching track and intensity of developed systems.....

Sails, Not real sure. Have not looked at many of the forecast maps or imagery. It has a circulation that looks to be just south of DR. The convection is also still increasing over this area. Have to watch it as the day progresses.

StormJunkie.com Quick Links for fast and easy access to the best free weather data on the web.
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802. SLU
12:50 PM GMT on July 30, 2006
thats right randrewl
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801. icepilot
12:49 PM GMT on July 30, 2006
Good morning all,

sorry, I mostly lurk as you guys are way ahead of me - I ws trained as an observer and short term weather guesser many, many years ago.

StormJunkie - thanks for the compiled links

to all who suffer from time zone demencia - Grin. Here's a nice US time link - it's java driven
Link

for the world's zones
Link

I used to chase Iceburgs in North Atlantic for the IIP and had to juggle with 3 different zones at same time and one (Newfoundland) is a 1/2 hour zone -Grin

Member Since: July 9, 2005 Posts: 0 Comments: 387
800. BoyntonBeach
12:49 PM GMT on July 30, 2006
Randrewl

Thanks! How ironic! I just logged on to see if there were any model runs of the current Blob!
Member Since: July 5, 2006 Posts: 0 Comments: 1
798. sails1
12:39 PM GMT on July 30, 2006
Thanks SJ for the information. They just couldn't use the Lat/Long? Too simple I guess! Well the area of distrubed weather NE of Rico is looking better organized; however, there is a slice of SW upper level winds that are fighting againest development. With that said, the last few frames do show those hostile winds starting to abate! SJ what are your thoughts on this developing weather system?
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796. SLU
12:38 PM GMT on July 30, 2006
the GFDL loves this 99L ... anyone seen the new 6z run?? .. it's even more agressive and leaves Florida very exposed too
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794. ricderr
12:32 PM GMT on July 30, 2006
good mornin good boys and girls..happy sunday to you
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792. StormJunkie
12:25 PM GMT on July 30, 2006
What's funny about the GFDL Rand? Did pretty well last year if I remember correctly.
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791. IKE
12:24 PM GMT on July 30, 2006
Personal opinion...odds are at least 1 of these 2 systems will develop. Hard to believe that one wouldn't.

Whether they make it to the USA is questionable.
Member Since: June 9, 2005 Posts: 23 Comments: 37858
789. StormJunkie
12:22 PM GMT on July 30, 2006
I am not sure all of that is right IKE, but the basic concept is. May be the NHC that issues it, may be the number range is a little different.
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788. StormJunkie
12:20 PM GMT on July 30, 2006
Lot's of ifs Rand, and there will be many more to come. My point was that the Bermuda high did not look strong enough in the current GFDL to prevent it from moving N and NE out to sea. Again, very, very, speculative, as I am not even convinced that it will develop.

The PR area will need to be watched today. Convection is starting to fire aroud the circulation, but I am not sure if it will persist.
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787. code1
12:20 PM GMT on July 30, 2006
oooops Good morning to all as well. Puerto Rico wave conditions for the next few days?
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785. code1
12:19 PM GMT on July 30, 2006
Thanks guys. Hope you all have a good day.
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784. IKE
12:18 PM GMT on July 30, 2006
I didn't know that SJ...wasn't familiar with invest before this hurricane season.

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783. SLU
12:15 PM GMT on July 30, 2006
i'm in St. Lucia
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782. StormJunkie
12:15 PM GMT on July 30, 2006
sails, 99L is the number that the Navy (i think) assigns to areas that are being investigated for development. The numbers run from 90L to 99L I think. THey restart after 99. That means that if the PR area were to become an invest it would be 90L, or maybe 91L.

I know I likely screwed up some of the specifics there, but that is it in a nutshell.
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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.