Hawaii braces for Felicia; 99L near the Cape Verdes Islands may develop
A strong tropical wave (99L) is just south of the Cape Verdes Islands, 800 miles off the coast of Africa. This morning's QuikSCAT pass showed a nearly closed surface circulation, stretched out along one axis. The satellite saw winds of up to 45 mph in a band of heavy thunderstorms well south of the Cape Verdes Islands. The islands have seen winds of only 10 - 15 mph and some occasional rain showers thus far from the disturbance. Heavy thunderstorm activity associated with 99L died down this morning, but appears to be making a comeback late this morning. Wind shear is moderate, about 10 knots, and sea surface temperatures are moderately warm, about 27 - 28°C. There is a large area of dry air to 99L's north that is interfering with the storm's organization, though.
Figure 1. Current satellite image of disturbance 99L.
Wind shear is expected to be moderate, 5 - 15 knots, through Wednesday. SSTs will remain relatively constant at 27°C, but the dry, stable air of the Saharan AIr Layer (SAL) to 99L's north will be problem for it. NHC has given 99L a moderate (30 - 50% chance) of developing into a tropical depression by Wednesday morning, which is a reasonable forecast. Most of the models show some weak development, but none of them predict 99L will become a hurricane. It is too early to say if 99L will recurve north of the Lesser Antilles Islands or not, since it will be at least 5 days before the storm makes it that far. It is unusual, though, for storms forming this far north to make it all the way across the Atlantic to hit the Lesser Antilles Islands.
The GFS and ECMWF models are predicting the possible development of a new tropical wave coming off the coast of Africa late this week.
Felicia continues to weaken, but is a flash flooding threat to Hawaii
Tropical Storm Felicia has weakened steadily over the past 24 hours, thanks to cool sea surface temperatures and increasing shear. Recent satellite loops show that strong upper-level winds from the west have pushed the storm's heavy thunderstorm activity to the northeast side of the center, exposing the surface center as a swirl of low clouds. Felicia's relatively meager heavy thunderstorm activity is steadily moving away from the center of the storm.
Figure 2. History of hurricane activity over Hawaii since 1950. Hawaii islands have been hit by only 9 tropical cyclones of tropical depression or greater strength, with 4 others passing withing 75 miles of an island. Image credit: NOAA Coastal Services Center.
Sea surface temperatures (SSTs) under Felicia are 25°C, well below the 26°C threshold typically needed to sustain a hurricane. SSTs will slowly increase to 26°C by Tuesday. Wind shear has increased to a high 30 knots, and is expected to increase further to 40 knots by Tuesday. The high shear combined with the cool SSTs should continue to weaken Felicia today. I give a 30% chance that the shear will completely rip away Felicia's heavy thunderstorm activity by the time the storm reaches Hawaii, leaving only a swirl of low-level clouds that will not cause significant flooding problems. The wind speed probabilities forecast shows about a 25% chance Felicia will still be a weak tropical storm at 3 am Hawaiian time Tuesday morning, and a 15% chance the storm will have dissipated. If Felicia does hold together that long, it would be only the tenth tropical cyclone of tropical depression or higher strength to affect the islands since 1950 (Figure 2). Large swells from Felicia are already affecting the Big Island, and a high surf warning has been posted for east-facing shores of the Big Island and other Hawaiian islands. Felicia or its remnants may bring heavy rain, flash flooding, and mud slides to the islands beginning this afternoon, and a Flash Flood Watch has been posted for most of the islands.
Links to follow:
Long range radar from the Big Island
Wundermap for Hawaii
I'll have an update Tuesday morning.
Reader Comments
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Yet again, the SAL is the culprit.
Agreed, too much SAL right now for any convection to pop up, give it some time guys.
Feature developing a lot of deep convection considering the immediate environment is some what dry. Structure seems to have improved also Link
Neuse River, New Bern, North Carolina (PWS)
Updated: 4 sec ago
93.0 °F
Clear
Humidity: 100%
Dew Point: 93 °F
Wind: 7.0 mphfrom the WSW
Wind Gust: 9.0 mph
Pressure: 30.00 in (Falling)
Heat Index: 149 °F
Visibility: 9.0 miles
UV: 10 out of 16
Clouds: Clear -
(Above Ground Level)
Elevation: 30 ft
no it is not SAL is too far north
Choked...badly. NHC had a discussion yesterday about that possibility happening....they said "dry-air".
Someone posted it on here...
Yup. Its going to take some time to redevelop.
Well im not sure if it will, but we'll see.
30-50 chance. is more like it, right now seems to torwards 30.
Yup.
The SAL killed it, look how it is surrounded!
Obs from Barbados. Pressure falling...winds from the NNW
Up at the top of this "Reader Comment" area there is a box on the right labeled "Filter". the way you describe your view the filter is probably not set at "Show all".
CRS
AOI/XX/XXL
MARK
13.3N/60.1W
I checked the SAL when Felicia was a monster. There was SAL similar to what you see around 99L. It surprised me.
by the images youve posted...99l is stacked pretty well and the barbados wave is good, except at the 500mb level...
whats the timestamps on these images...i want to see what the next set that come out look like...
50-50 simply means it will or it won't and thats what will happen it either will or won't.
On hot SSTs it could feast!
Yet there's SAL up above
That will show it no love
A TD at the very least?
http://www.nco.ncep.noaa.gov/pmb/nwprod/analysis/carib/gfs/12/index_pcp_s_loop.shtml
Thanks a lot..it was an easy fix and right in front of me!! I just signed up, I have been lurking for a couple of years with just a few posts..looking forward to the rest of hurricane season 09'
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
251 PM EDT MON AUG 10 2009
EXTENDED OUTLOOK: THE EMPIRICAL WAVE PROPAGATION MODELS MAINTAINS
GOOD CONTINUITY WITH PREVIOUS FORECASTS...SHOWING MJO CONDITIONS
ACROSS NORTHERN SOUTH AMERICA INTO THE TROPICAL ATLANTIC IMPROVING
THROUGH MID AUGUST...WITH CONDITIONS TO REMAIN FAVORABLE THROUGH
THE END OF THE MONTH-FIRST WEEK IN SEPTEMBER. THE GLOBAL MODELS
ARE STARTING TO REACT TO THE CHANGE IN CONDITIONS/
ENVIRONMENT...AS THEY NOW SHOW RISK OF WARM CORE CYCLOGENESIS ON
BOTH OCEANS. AT UPPER LEVELS A CELL OF THE SUBTROPICAL RIDGE WILL
MEANDER NORTH OF THE GREATER ANTILLES/OFF THE COAST OF THE
USA...WHICH IS TO THEN SUSTAIN A TROUGH OVER THE CENTRAL ATLANTIC.
A WEAK/NARROW RIDGE IS TO THEN REMAIN TO THE SOUTH OF 23N. IF THIS
PATTERN PERSIST...TROPICAL CYCLONES FORMING OFF THE COAST OF
AFRICA ARE LIKELY TO TURN TOWARDS THE NORTH AS THEY ARE ABOUT TO
REACH THE ISLAND CHAIN. THE ONES FORMING TO THE WEST OF 45W ARE UP
FOR GRAB...AS THEY ARE LIKELY TO THREATEN THE ISLAND CHAIN-PUERTO
RICO/DOMINICAN REPUBLIC.
18z update become red T # 2.0
Viewing: 801 - 851
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