African tropical wave 99L slowly organizing

By: Dr. Jeff Masters , 1:26 PM GMT on July 31, 2012

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A tropical wave (Invest 99L) near 9°N 41°W, halfway between the Lesser Antilles Islands and the coast of Africa, has the potential to develop into a tropical depression later this week as it moves westward at 10 - 15 mph. Visible satellite loops show that the disturbance now has a moderate amount of poorly-organized heavy thunderstorms that continue to slowly increase in intensity and areal coverage. There is no surface circulation, but some counter-clockwise rotation of the large-scale cloud pattern is evident. Water vapor satellite loops show that 99L has a reasonably moist environment. The latest Saharan air layer analysis shows that the dry air from the Sahara lies to the north of 99L and is currently not affecting the storm. WInd shear over the disturbance is a light 5 - 10 knots, and ocean temperatures are 28°C, (82°F) which is well above the 26.5°C (80°F) threshold typically needed to allow formation of a tropical depression.


Figure 1. Morning satellite image of Invest 99L.

Forecast for 99L
Wind shear is expected to remain light through Friday, and ocean temperatures will remain near 28°C, according to the 8 am EDT run of the SHIPS model. However, a band of high wind shear of 20 - 40 knots associated with the subtropical jet stream lies just to the north of 99L, and it would not be a surprise to see 99L experience some higher shear conditions than are currently forecast. The farther north 99L gets, the higher the shear it will experience, and the SHIPS model is predicting shear in the moderate range, 10 - 20 knots, for Saturday - Sunday, as the storm works its way to 15°N. The disturbance is at 9°N, which is close enough to the Equator that the storm will have some difficultly getting spinning. Most of the models are showing some slow development of 99L. There are some major differences in the predicted forward speed of 99L, with the ECMWF and UKMET models predicting the storm will reach the Lesser Antilles on Friday, and the GFS predicting a later arrival, on Saturday. At 8 am Tuesday, NHC gave 99L a 20% chance of developing into a tropical depression by Thursday morning. I expect the storm will begin having trouble with tendrils of dry air reaching down from the north at times this week, but give 99L a 50% chance of eventually developing into Tropical Storm Ernesto sometime in the next ten days. Residents and visitors to the Lesser Antilles Islands should anticipate heavy rains and strong winds from 99L beginning to affect the islands as early as Friday morning. The long-range fate of 99L next week is uncertain. A track west to west-northwest through the Caribbean, or to the northwest towards the U.S. East Coast are both possible. The storm is less likely to survive if it heads northwest towards the U.S.

Extreme heat in the Central U.S.
The withering heat in America's heartland continued on Monday, with high temperatures of 112° recorded in Winfield, Kansas and Searcy, Arkansas. Little Rock, Arkansas hit 111°, their 3rd hottest temperature ever record, behind the all time record of 114° set just last year on August 3, and the 112° reading of 7/31/1986. Wichita and Coffeyville in Kansas both hit 111° Monday, and in Oklahoma, Enid, Tulsa Jones Airport, and Chandler all topped out at 111°. Carr Creek, Missouri hit 110°, the hottest temperature measured in the state so far this year. Highs temperatures Tuesday and Wednesday in this region could reach 110° again, as the most extreme heat this week will stay focused over Oklahoma and surrounding states.

Jeff Masters

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Quoting wxchaser97:
Yeah now I see, thanks for pointing that out.


Take a look at the shortwave loop

This is one of the best ways to determine where the center is. It shows up quite nicely between the 9 and 10 degree N lat. line. Check the lat/lon box and then zoom in when you run the loop
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Quoting Grothar:
Nice shot of 99L.




Looks very close to Ernesto right now.
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Quoting Bluestorm5:


Almost a tropical depression.


But the NHC just 3 hours ago gave it a 30% chance of becomming a depression in the next 2 days.
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Quoting MississippiWx:
Not sure that 99L is "moving northwest." It appears to be a center consolidation further NW than the coordinates from earlier. In fact, the center is most likely further north and west than the 18z coordinates.


Yeah I agree more of a relocation out of the ITCZ. Watch the CMC model peg this system. Going to get very interesting across the Caribbean and the US over the coming days as 99L could track right up into FL early to mid next week.
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Nice shot of 99L.


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Quoting kmanislander:


That is not NW, just barely due N of West which is essentially W for the NHC
Yeah now I see, thanks for pointing that out.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
Hopefully if 99L will stay away from Jamaica if it develops into a strong TS or hurricane. Work is now in progress on the Palisadoes shoreline protection to reduce the beach erosion and damage from storms and hurricanes...the project is slated for completion in December of this year.

Palisadoes is the thin strip of land connecting one of our airports to the mainland.

Palisadoes after hurricane Ivan

on going work


The road will be raised from its existing levels of 0.6 %u2013 1.0 metre, to 2.4 - 3.2 metres above sea level.
Rehabilitative and protective works along the Peninsula have been designed for a 100-Year Return Period (i.e. the shoreline will be expected to withstand storm surges only anticipated to re-occur every 100 years). A design rainfall intensity of 178mm per 24 hours was utilized in this design.
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.................................three places to watch
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i don't know how to post the visual of this loop, but go here Link to see how the moisture field is really tightening in on 99L in last few frames.. the invest is definitely consolidating now, but at it's own detriment perhaps.
an airmass to the south, as Levi stated, looks to be a significant swath of dry air.
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Quoting wxchaser97:
Winds increased from 20 knots to 25 knots and its still moving NW. Should be a TD soon.


That is not NW, just barely due N of West which is essentially W for the NHC
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But it going up all day now it at 9.6N!!
00 GMT 07/31/12 8.9N 36.6W
12 GMT 07/31/12 9.3N 39.6W
18 GMT 07/31/12 9.6N 41.3W
Quoting CorfidiFan:
nop
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Not sure that 99L is "moving northwest." It appears to be a center consolidation further NW than the coordinates from earlier. In fact, the center is most likely further north and west than the 18z coordinates.
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Quoting Grothar:


I won't :)

you know i'm just playing you to build cred around here.. i knew you'd take the bait!!
:P
in actuality, the SAL you posted doesn't look all that offensive to tropical development, but i do think development will be hindered by a lack of widely available precipitable moisture.. if it were closer to that wave west, a lot of factors would change, imo.
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Quoting Tazmanian:



is there a point that you keep on reposting that?



i can post what i like here bud
and it the latest info from navy
if a TCFA is to show up
it will be there first

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99L my go FL?!?!?
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Here is the current timetable for 99L in terms of westward movement. It has a nice window of opportunity before it gets squeezed between the TUTT cell and land mass of South America in around 72 hours:



TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
226 PM EDT TUE JUL 31 2012

PERTURBATIONS IN THE EASTERLIES...INITIALIZED AT 12UTC

INITIAL 24 36 48 60 72 84 TYPE
41W 44W 46W 49W 52W 55W 58W TW
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I thought I hit modify comment instead of quote.
Oh well, one last view of 99L and then I'm really gone.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
It going NW!:)
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Quoting 34DDHaboobs:


CSB...I used to run the "gun" for a 2-man land surveying crew. On a 108 degree day, where a popcorn shower hit the gully we were in on Lake Travis (Austin, TX), with no wind at all and a soon-after blazing sun, my $50K laser read a 147 degree heat index (100% accurate). I drank 2.5 gallons of water that day, and it all came out via sweat.

On Lake Travis we've been getting massive, destructive microbursts lately that I've never seen before. Flipping over 10-slip marinas with boats moored and blew down a quartet of huge old red oaks.
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Quoting JLPR2:



31/1745 UTC 9.2N 42.1W T1.0/1.0 99L -- Atlantic

Satellite estimates always see the center somewhere else, but look, a T# at 1.0.




so i wounder oh is right ?
Member Since: May 21, 2006 Posts: 5091 Comments: 114728
99L will go north some in order to survive anyway and get into the Caribbean, not that it's going to plow north of the islands but dead aim into it.
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Quoting StormTracker2K:


I agree it stays in the Caribbean but north of the guidance but similar to that of the CMC model.

Nah, south of that but not right above S.A. somewhere in the middle.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
Thx Levi!!:)
Quoting Levi32:


I will have one tomorrow morning.

Getting back to work now. Later all.
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Quoting SFLWeatherman:
Are you doing a Tropical Tidbit today???


I will have one tomorrow morning.

Getting back to work now. Later all.
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Quoting Tazmanian:
AL, 99, 2012073118, , BEST, 0, 96N, 413W, 25, 1010, DB,
Winds increased from 20 knots to 25 knots and its still moving W. Should be a TD soon.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
Quoting hydrus:
It is starting to look like September out there.


Right!!! Like I said, I am sticking to my original figures I made in April.
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just to note..if something does form off the SE coast, and 99L does strength rapidly, we may have another player in influence steering??
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934. JLPR2
Quoting Tazmanian:
AL, 99, 2012073118, , BEST, 0, 96N, 413W, 25, 1010, DB,



31/1745 UTC 9.2N 42.1W T1.0/1.0 99L -- Atlantic

Satellite estimates always see the center somewhere else, but look, a T# at 1.0.
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Quoting Bluestorm5:


Almost a tropical depression.



yep
Member Since: May 21, 2006 Posts: 5091 Comments: 114728
SO it is at 9.6N!!!! it going UP we my have a TD or TS by 5 am tomorrow!!!!
00 GMT 07/31/12 8.9N 36.6W
12 GMT 07/31/12 9.3N 39.6W
18 GMT 07/31/12 9.6N 41.3W
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Quoting wxchaser97:
I'm one who is disagreeing with that, I think 99L will stay in the Caribbean.


I agree it stays in the Caribbean but north of the guidance but similar to that of the CMC model.
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Looks like 99L might make a run at Ernesto tomorrow morning:

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......................futurecast has nothing real in the gulf thru this friday..but look all the way to the lower right
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Quoting Grothar:


They never listen to us, Storm! :):)


It's going to be heading into much warmer water of the coming days so a hurricane coming into the Caribbean seems to be a good bet to me. I remember this same situation with Ivan when many on here just didn't get it. Very similar to Ivan in regards to location and this will be a dangerous storm down the road I believe.

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Quoting Tazmanian:
AL, 99, 2012073118, , BEST, 0, 96N, 413W, 25, 1010, DB,


Almost a tropical depression.
Member Since: August 1, 2011 Posts: 28 Comments: 7903
Quoting Tropicsweatherpr:


You think TCFA will be issued tonight?
maybe if not it never will
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Quoting JLPR2:
Almost D-min for 99L. After that 99L should start to explode and things should get interesting.



Sun is down near 25W.


It has to diurinate first.
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AL, 99, 2012073118, , BEST, 0, 96N, 413W, 25, 1010, DB,
Member Since: May 21, 2006 Posts: 5091 Comments: 114728
Quoting StormTracker2K:


I know some elite on here will disagree but 99L is taking off right now based on satellite. 99L is destin to take a more northerly track as it does appear to be wrapping up nicely now.

I'm one who is disagreeing with that, I think 99L will stay in the Caribbean.
Member Since: March 16, 2012 Posts: 127 Comments: 7927
................................east coast get ready..up and down the whole coastline in a few
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Quoting StormTracker2K:


I know some elite on here will disagree but 99L is taking off right now based on satellite. 99L is destin to take a more northerly track as it does appear to be wrapping up nicely now.

The steering is favorable for southern path...
Member Since: August 1, 2011 Posts: 28 Comments: 7903

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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.