African tropical wave 99L slowly organizing

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

Share this Blog
38
+

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

Reader Comments

Comments will take a few seconds to appear.

Post Your Comments

Please sign in to post comments.

or Join

Not only will you be able to leave comments on this blog, but you'll also have the ability to upload and share your photos in our Wunder Photos section.

Display: 0, 50, 100, 200 Sort: Newest First - Order Posted

Viewing: 271 - 221

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48Blog Index

Good Morning to All From America's Left Coast
Member Since: September 18, 2010 Posts: 0 Comments: 5133
12Z GFS 24hrs.
Member Since: October 26, 2011 Posts: 0 Comments: 2651
Quoting TropicalAnalystwx13:
If you look at the Caribbean false color RGB loop...trade winds aren't strong at all in the Caribbean. This is supported by buoy data.

Link


They might not be quite as strong as a week or 2 ago...but they are there. You can see the trade winds blowing those clouds in the S Caribbean W to E. There is enough to inhibit development. Looking at satellite you can still see some dry air in that region as well. The bottom line it's just too stable in the W Atlantic for things to really take off. I believe we are at the beginning stages for a very busy August. The MJO is really going to kick off the fireworks in a couple of weeks imo.
Member Since: Posts: Comments:
Quoting CybrTeddy:
As mentioned, first thing that 99L needs to do is detach from the ITCZ. While systems can certainly develop within the ITCZ, they cannot be sustained by it, like a frontal low of sorts, same general principle. When that happens, convection will begin to take a noticeable downtake in coverage but as long as the models are showing some consistency we may have something if it can develop before reaching ~50-55W or so. There's no chance that if 99L makes it into the Caribbean it will survive, the trade winds caused by the developing El Nino is far too intense. It needs to thread the needle with the islands to survive. The GFS, CMC, NOGAPS, HWRF and GFDL have all been showing this developing into a moderate Tropical Storm. It will probably be a similar situation to Tropical Storm Colin in 2010. There's very little chance of this becoming a major system. We'll probably have something like in 2009 with a explosion of activity once the MJO comes around in mid-August.

Read back on the blog a bit.

Oh, and Dr. Masters,

"The storm is less likely to survive if it heads northwest towards the U.S."
Member Since: July 6, 2010 Posts: 113 Comments: 31497
July 2012 was one of the hottest months on record around the Lower Great Lakes region. I compiled a list of the hottest Julys for the region. 2012 looks to be in the top three for this region, for sure. Other hot Julys in the region include 2011, 1955, & 1921. Further west, the Dust Bowl summers of 1934 & 1936 also show up as very hot Julys.

http://www.wunderground.com/blog/ClimateChange/sh ow.html
Member Since: Posts: Comments:
12z GFS is running...

Money is on "Death By Caribbean"
Member Since: Posts: Comments:
As mentioned, first thing that 99L needs to do is detach from the ITCZ. While systems can certainly develop within the ITCZ, they cannot be sustained by it, like a frontal low of sorts, same general principle. When that happens, convection will begin to take a noticeable downtake in coverage but as long as the models are showing some consistency we may have something if it can develop before reaching ~50-55W or so. The GFS, CMC, NOGAPS, HWRF and GFDL have all been showing this developing into a moderate Tropical Storm. It will probably be a similar situation to Tropical Storm Colin in 2010. There's very little chance of this becoming a major system. We'll probably have something like in 2009 with a explosion of activity once the MJO comes around in mid-August.
Member Since: Posts: Comments:
Quoting Patrap:
accu, without JB is just weather.
joe.sobel.and.the.other.guy.from.acc/that.just.ac cidently.died..their.free.clips.were.the.best!
Member Since: Posts: Comments:
Quoting GeorgiaStormz:


passed my house already, im not expecting too much this afternoon.
Not even in a SLGT any more
..its only the first wave,more to come
Member Since: August 6, 2011 Posts: 4 Comments: 36929
Member Since: July 6, 2010 Posts: 113 Comments: 31497
Jogged to the south just in time to miss downtown.
Quoting islander101010:
lucky.the.eye.didnt.go.over.miami

Member Since: Posts: Comments:
Chances of 99 reaching hurricane status remains below 10 percent based on historical data.
Member Since: Posts: Comments:
Quoting LargoFl:


passed my house already, im not expecting too much this afternoon.
Not even in a SLGT any more
Member Since: February 11, 2012 Posts: 0 Comments: 9720
Conditions are actually becoming more favorable out ahead of 99L, thus being the reason the first wave did not die, in fact, it's organizing under 5-10 knots of wind shear. Trade winds are not as strong as initially thought. Complete opposite of our thinking yesterday.. In order for 99L to continue, it has to stay in the Caribbean.. You can even see an anticyclone waiting to catch it..


EDIT: An anticyclone is already over 99L...
Member Since: Posts: Comments:
Quoting GeorgiaStormz:


no its calm today
Member Since: August 6, 2011 Posts: 4 Comments: 36929
Quoting TropicalAnalystwx13:
If you look at the Caribbean false color RGB loop...trade winds aren't strong at all in the Caribbean. This is supported by buoy data.

Link


Yeah I think we may have a strong system crusing thru the Caribbean. I think we can give thanks to this wave near PR for paving the way for 99L.

Member Since: October 26, 2011 Posts: 0 Comments: 2651
Member Since: August 6, 2011 Posts: 4 Comments: 36929
Quoting LargoFl:
..bad weather coming towards you today


no its calm today
Member Since: February 11, 2012 Posts: 0 Comments: 9720
Quoting GeorgiaStormz:
I so want this program :P
..bad weather coming towards you today
Member Since: August 6, 2011 Posts: 4 Comments: 36929
I so want this program :P
Member Since: February 11, 2012 Posts: 0 Comments: 9720
Member Since: Posts: Comments:
Someone has learned how to use the RAMMB page me tinks.

: )
Member Since: Posts: Comments:
If you look at the Caribbean false color RGB loop...trade winds aren't strong at all in the Caribbean. This is supported by buoy data.

Link
Member Since: July 6, 2010 Posts: 113 Comments: 31497










Member Since: September 30, 2007 Posts: 9 Comments: 15932
I did a tropical update early this morning on my blog (which always covers all corners of the Atlantic basin)...check it out if you want...
Member Since: Posts: Comments:
AMSU Radial/Height Cross Sections



Member Since: Posts: Comments:
Quoting unknowncomic:
20 years ago this year, the baddest storm to hit SFLA in my lifetime, Andrew,

sent us into a surreal sense of impending doom here in south florida. It will be

interesting to me how the anniversary goes-AUG.24th.
lucky.the.eye.didnt.go.over.miami
Member Since: Posts: Comments:
The image that was posted above shows dry air is still a problem as well. It's enough to keep things in check. The best models(GFS and ECMWF) were never thrilled with this system from the start. They were sniffing out conditions ahead of 99L.
Member Since: Posts: Comments:
Quoting robert88:


The trade winds are fierce in that region because of a developing el nino.


Negative.



Member Since: Posts: Comments:
I think at 2pm
99L will be at 30%
The Wave behind it will be at 10-20% (new 90L)
Member Since: Posts: Comments:
Oye...

SST's mean absolutely nothing when you have hostile conditions. Vertical instability is below normal and the UA pattern looks less than impressive. The only thing that this has going for it is that a Kelvin Wave will be moving over 99L in a day or two and enhance convection for a bit.

(Das Blue)



If this can't develop before 55W, then it's best hope is to make it into the GOM in 8-10 days.
Member Since: Posts: Comments:


Member Since: September 30, 2007 Posts: 9 Comments: 15932
Member Since: August 6, 2011 Posts: 4 Comments: 36929
SPC today's outlook


I think they are going to have to increase the area especially for AL
Member Since: August 19, 2006 Posts: 13 Comments: 14548
Looks like 99L is Caribbean bound.


000
FXUS62 KMFL 311408
AFDMFL

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MIAMI FL
ISSUED 242 AM EDT TUE JUL 31 2012

A TROPICAL WAVE OVER THE LEEWARD ISLANDS AND PUERTO RICO WILL MOVE
TOWARDS CUBA AND THE BAHAMAS ON THURSDAY. PWATS ARE STILL EXPECTED
TO REMAIN AROUND THE 25TH PERCENTILE...SO POPS WILL REMAIN
RELATIVELY LOW. ISOLATED CONVECTION IS EXPECTED FOR THE METRO AREAS
AND SCATTERED STORMS ACROSS THE INTERIOR. THE LEADING EDGE OF THE
TROPICAL WAVE MAY MOVE INTO SOUTH FLORIDA AROUND DAYBREAK ON
FRIDAY...WITH PWATS INCREASING TO AROUND 2 INCHES BY THE AFTERNOON.
SO INCREASING RAIN CHANCES ARE EXPECTED FRIDAY AND SATURDAY AS THE
WAVE MOVES ACROSS THE REGION...WITH SCATTERED TO POSSIBLY NUMEROUS
SHOWERS AND STORMS. STRONG HIGH PRESSURE IS EXPECTED TO BUILD
ACROSS THE WESTERN ATLANTIC AND THE SOUTHEAST ON SUNDAY...WITH
DEEP EASTERLY FLOW RETURNING TO THE REGION.
THIS WILL LEAD TO
ISOLATED TO WIDELY SCATTERED STREAMER SHOWERS IN THE MORNING FOR
THE EAST COAST...WITH SCATTERED STORMS MOVING TO THE INTERIOR AND
GULF COAST IN THE AFTERNOON HOURS FOR SUNDAY INTO EARLY NEXT WEEK.
TEMPS WILL REMAIN NEAR NORMAL THROUGH THE PERIOD.
Member Since: Posts: Comments:
Quoting robert88:


The trade winds are fierce in that region because of a developing el nino.


I'm Not very sure, is because el nino
Member Since: Posts: Comments:
Quoting stormchaser19:


which path you choose ?
a) GFS
b) ECMWF
c) NOGAPS
d) CMC
e) MY PATH

I choose e) LOL


(a+b)/2
Member Since: February 11, 2012 Posts: 0 Comments: 9720
accu, without JB is just weather.
Member Since: Posts: Comments:
Storm Relative 1km Geostationary Visible Imagery

Member Since: Posts: Comments:
Quoting AussieStorm:

I choose F5. lol.

I meant G xD
Member Since: Posts: Comments:
from accuweather..........
Severe Storm Risk: Atlanta, Tallahassee, Jacksonville



Jul 31, 2012; 8:42 AM ET

More Sharing ServicesShare | Share on facebook Share on myspace Share on google Share on twitter
.


Rounds of gusty thunderstorms will blow through parts of the South today.

Cities in the crosshairs of this wild weather include Atlanta, Tallahassee, Jacksonville, Columbia, Montgomery, Pensacola, Charleston, Macon and Wilmington.

There will be two or even three rounds of powerful storms.

The first round will come this morning across central and southern Alabama and western Georgia as a complex of strong storms from overnight moves over the area.

The second round of thunderstorms will come this afternoon as the air heats up and mixes with the tropical humidity all ready in place. This round will affect areas farther east and south over much of Georgia, South Carolina and the Florida Panhandle.



The fiercest storms will produce damaging blasts of wind, frequent and deadly lightning, hail larger than the size of quarters and blinding downpours.

Flash flooding is even likely in areas that have especially slow-moving storms or storms that repeat over and over.

Be sure to heed any watches or warnings that may be issued, and know what the difference is.

If a watch is issued, this means the potential for a dangerous thunderstorm is high, but the threat is not imminent. If a warning is issued, this means a dangerous thunderstorm is imminent, and you should take shelter immediately.
Member Since: August 6, 2011 Posts: 4 Comments: 36929
Storm Relative 16km Geostationary Water Vapor Imagery

Member Since: Posts: Comments:
Quoting quasistationary:


Why will it die in the Caribbean?


The trade winds are fierce in that region because of a developing el nino.
Member Since: Posts: Comments:
Member Since: Posts: Comments:
Quoting ilovehurricanes13:
its getting better looking now..

Sure is.


Member Since: Posts: Comments:

Viewing: 271 - 221

Page: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 | 28 | 29 | 30 | 31 | 32 | 33 | 34 | 35 | 36 | 37 | 38 | 39 | 40 | 41 | 42 | 43 | 44 | 45 | 46 | 47 | 48Blog Index

Top of Page

About

Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.

Local Weather

Overcast
62 °F
Overcast