[Tropical] Tropical Weather Discussion

[EMWIN Server]

AXNT20 KNHC 262358
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI AUG 26 2005

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHEASTERN SECTIONS
OF SOUTH AMERICA...AND ATLANTIC OCEAN TO THE AFRICAN COAST FROM
THE EQUATOR TO 32N. THE FOLLOWING INFORMATION IS BASED ON
SATELLITE IMAGERY...WEATHER OBSERVATIONS...RADAR...AND
METEOROLOGICAL ANALYSIS.

BASED ON 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...
THE CENTER OF HURRICANE KATRINA IS NEAR 24.7N 83.3W AT 27/0000
UTC ABOUT 70 NM W OF KEY WEST MOVING WSW 6 KT. THE ESTIMATED
MINIMUM CENTRAL PRESSURE IS 965 MB. THE MAXIMUM SUSTAINED WINDS
ARE 85 KT WITH GUSTS TO 105 KT. PLEASE REFER TO THE LATEST NHC
FORECAST/ADVISORY UNDER AWIPS/WMO HEADERS MIATCMAT2/WTNT22 KNHC
AND THE PUBLIC ADVISORY UNDER HEADERS MIATCPAT1/WTNT32 KNHC FOR
MORE DETAILS.  THE HURRICANE CONTINUES TO GET BETTER-ORGANIZED
WITH EARLIER RECON REPORTS SHOWING A STEADY PRESSURE DROP AND
LAST VISIBLE SATELLITE PICTURES HAVING HINTS OF AN EYE.  UPPER
OUTFLOW IS STRONG TO THE SOUTH AND IS GRADUALLY EXPANDING TO THE
NORTH.  THIS HURRICANE POISES A SERIOUS THREAT TO THE USA GULF
COAST WITH VERY WARM WATER AND LIGHT SHEAR IN ITS PATH.
SCATTERED TO NUMEROUS STRONG CONVECTION IS WITHIN 90 NM IN THE N
SEMICIRCLE AND 180 NM IN THE SRN SEMICIRCLE.

1008 MB LOW IS IN THE CENTRAL ATLC NEAR 20N48W MOVING NW 10 KT.
THE SYSTEM HAS BEEN UNDER CONSTANT MODERATE TO STRONG WLY SHEAR
FOR DAYS BUT IT APPEARS THE CENTER IS REFORMING CLOSER TO THE
DEEP CONVECTION.  THE LACK OF A WELL-DEFINED CENTER HAS BEEN THE
ONLY HINDRANCE TO THIS SYSTEM BECOMING A TROPICAL CYCLONE WITH
PLENTY OF TSTMS NE OF THE CENTER.  ALTHOUGH THE SHEAR IS
FORECAST TO REMAIN UNFAVORABLE FOR STRONG DEVELOPMENT... IT IS
POSSIBLE THE SYSTEM WILL BECOME A TROPICAL CYCLONE DURING THE
NEXT COUPLE OF DAYS.

...TROPICAL WAVES...
CENTRAL ATLC WAVE IS ALONG 37W S OF 17N WITH A 1010 MB LOW NEAR
11N37W MOVING W 5-10 KT.  THIS LOW PRESSURE AREA IS ON A SLOW
DEVELOPMENT TREND WITH A LARGE CIRCULATION NOTED ON VISIBLE
SATELLITE PICTURES AND A FEW BANDING FEATURES.  TSTMS REMAIN
DISORGANIZED AROUND THE CENTER BUT UPPER-LEVEL WINDS ARE
FAVORABLE FOR DEVELOPMENT. COMPUTER MODELS ALSO SUGGEST THIS
AREA COULD BECOME A SUSPECT AREA FOR TROPICAL GENESIS AS THE
SYSTEM NEAR 20N48W MOVES NORTHWARD.  MOISTURE FROM THIS WAVE
COULD AFFECT THE LESSER ANTILLES IN THE MIDDLE OF NEXT WEEK.
WIDELY SCATTERED MODERATE CONVECTION FROM 10N-14N BETWEEN
32W-41W.

W CARIBBEAN WAVE IS ALONG 86W S OF 20N MOVING W 15 KT.
LONG-RANGE LOOPS SHOW THE WAVE AXIS NOW OVER CENTRAL AMERICA..
HELPING TO FORM SCATTERED TSTMS OVER LAND.  NO SIGNIFICANT
CONVECTION OVER WATER.

...ITCZ...

THE ITCZ AXIS IS ALONG 15N17W 14N33W.  THE ITCZ IS ILL-DEFINED W
OF 35W.  WIDELY SCATTERED MODERATE CONVECTION IS WITHIN 45 NM OF
LINE 14N30W TO 11N35W.


...DISCUSSION...
GULF OF MEXICO...
THE CIRCULATION OF KATRINA IS BEGINNING TO DOMINATE THE ENTIRE
GULF WITH NLY SURFACE WINDS OBSERVED AS FAR W AS JUST OFFSHORE
OF TEXAS ALONG 95W.  SIGNIFICANT RAINBANDS ARE SLOWLY EXITING
THE FLORIDA KEYS WITH A FEW FORMING IN THE TAMPA AREA.  ISOLATED
TSTMS ARE W OF THE HURRICANE FROM 21N-28N BETWEEN 86W-94W.  IN
THE UPPER LEVELS.. A MID/UPPER HIGH IS CENTERED NEAR VICKSBURG
MISSISSIPPI RIDGING E THRU SE GEORGIA AND WESTWARD THRU TEXAS.
THIS IS KEEPING THE HURRICANE MOVING WESTWARD.  MOST COMPUTER
MODELS SLOWLY WEAKEN THIS RIDGE WHICH COULD ALLOW THE HURRICANE
TO MOVE MORE NORTHWARD.  DIURNAL TSTMS ARE FORECAST TO BE
ENHANCED NEAR TALLAHASSEE TOMORROW AS MOISTURE FROM KATRINA
INCREASES.  IN ADDITION MOISTURE FROM KATRINA SHOULD SLOWLY
OVERSPREAD THE GULF COAST ON SAT FROM E TO W... IMPACTING SE
LOUISIANA BY SUN.

CARIBBEAN SEA...
CONVECTION FROM HURRICANE KATRINA EXTENDS ACROSS W CUBA INTO THE
NW CARIBBEAN...W OF 80W N OF 20N.   LARGE-SCALE UPPER HIGH
PRESSURE CONTROLS THE REGION WITH GENERAL NE TO E WINDS
THROUGHOUT THE CARIBBEAN.  AN UPPER TROUGH IS JUST N OF PUERTO
RICO COULD SLIGHTLY INCREASE THE CHANCE OF RAIN NEAR THAT ISLAND
OVERNIGHT... OTHERWISE TYPICAL CONVECTIVE REGIME IN PLACE.  WEAK
LOW-LEVEL TROUGH IS PRODUCING WIDELY SCATTERED TSTMS WITHIN 120
NM OF 15N67W WITH ONLY ISOLATED SHOWERS/TSTMS OVER THE REST OF
CARIBBEAN WATERS.  DIURNAL TSTMS LOOK TO BE ENHANCED OVER THE
GREATER ANTILLES W OF PUERTO RICO FOR AT LEAST THE NEXT SEVERAL
DAYS WITH HIGH LEVELS OF DEEP-LAYERED MOISTURE.  SEASONABLE
TRADEWIND SHOWERS ARE LIKELY FOR THE LESSER ANTILLES IN THE NEXT
COUPLE OF DAYS WITH LIMITED MOISTURE ALOFT.  THE ITCZ IS VERY
FAR TO THE NORTH JUST S OF SAN ANDRES ISLAND TO NW COLOMBIA.

ATLANTIC OCEAN...
UPPER-LEVEL RIDGING EXTENDS EASTWARD INTO THE W ATLC TO ABOUT
72W WITH A WEAKENING STATIONARY FRONT ALONG 31N/32N W OF 70W.  A
FEW TSTMS ARE FORMING OFFSHORE OF GEORGIA ALONG THAT FRONT NEAR
31N80W.  A COUPLE OF LARGE-SCALE MODELS ARE SHOWING THE
POTENTIAL FOR A LOW TO GENERATE NEAR THE FRONT AND MOVE SLOWLY
EASTWARD...PERHAPS ACQUIRING SOME TROPICAL CHARACTERISTICS WITH
TIME.  THIS GENESIS SEEMS LIKE IT WOULD BE SLOW TO OCCUR WITH
STRONG SHEAR FORECAST.  FARTHER E... A DEEP TROUGH IN THE
MID/UPPER LEVELS EXTENDS SOUTHWARD FROM JUST E OF BERMUDA NEAR
32N63W TO 19N65W WITH INSTABILITY ALONG THE TROUGH AXIS
PRODUCING ISOLATED TSTMS WITHIN 60 NM OF THE AXIS.  SECOND UPPER
TROUGH IS ALONG 51W N OF 18N... RESPONSIBLE FOR SHEARING THE LOW
NEAR 20N48W.  THIS TROUGH IS FORECAST TO WEAKEN WITH TIME...
WHICH COULD LESSEN THE SHEAR AND ALLOW THE SYSTEM TO DEVELOP.
IN THE E ATLC...A SERIES OF CUTOFF UPPER LOWS HAS BEEN NEARLY A
CONSTANT FEATURE FOR THE LAST FEW WEEKS.. WITH THE LATEST LOW
NEAR 32N22W.  FARTHER S... UPPER RIDGING HAS MOVED TO 16N W OF
THE CAPE VERDE ISLANDS WITH MODEST ELY SHEAR S OF THE RIDGE
AXIS.  THE RIDGE IS COMPRISED OF TWO UPPER HIGHS... ONE NEAR
16N57W AND THE OTHER AROUND 17N38W.  THE SHEAR IS FORECAST TO
REMAIN LOW IN THE TROPICS FOR THE WEEKEND WHICH COULD ALLOW THE
SYSTEM NEAR 11N376W TO FURTHER DEVELOP.

$$
BLAKE



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