[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 281038
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 AM EDT SAT 28 AUG 2004

TROPICAL WEATHER DISCUSSION FOR NORTH AMERICA...CENTRAL
AMERICA...GULF OF MEXICO...CARIBBEAN SEA...NORTHERN 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 0600 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
1045 UTC.

...SPECIAL FEATURES...
TROPICAL DEPRESSION SEVEN IS CENTERED NEAR 31.2N 78.4W AT
28/0900 UTC WITH MAXIMUM SUSTAINED WINDS OF 30 KT GUSTING TO 40
KT.  ESTIMATED MINIMUM CENTRAL PRESSURE IS 1011 MB WITH THE
DEPRESSION NEARLY STATIONARY. SEE THE LATEST NHC PUBLIC ADVISORY
OR FORECAST/ADVISORY ISSUED UNDER AWIPS/WMO HEADERS MIATCPAT2/
WTNT32 KNHC OR MIATCMAT2/ WTNT22 KNHC FOR MORE DETAILS.
SATELLITE IMAGES AND RADAR FROM CHARLESTON SC SUGGEST THAT THE
CLOUD PATTERN ASSOCIATED WITH THE DEPRESSION IS A LITTLE BETTER
ORGANIZED THEN EARLIER THIS MORNING.  AS THE RIDGE BEGINS TO
RE-DEVELOP TO THE NORTH THE DEPRESSION WILL BEGIN TO SLOWLY MOVE
TOWARD THE NW.  THE SYSTEM IS LIKELY TO BECOME A TROPICAL STORM
LATER TODAY.

HURRICANE FRANCES IS CENTERED NEAR 17.0N 51.3W AT 28/0900 UTC
MOVING NW 10 KT.  MAXIMUM SUSTAINED WINDS OF 100 KT WITH GUSTS
TO 120 KT. ESTIMATED MINIMUM CENTRAL PRESSURE IS 962 MB.  SEE
THE LATEST NHC FORECAST/ADVISORY ISSUED UNDER AWIPS/ WMO HEADERS
MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS.  THERE IS LITTLE OVER
ALL CHANGE IN THIS SYSTEM FROM PEARLER TODAY.  THE EYE IS NOT AS
STRONG AS IT WAS EARLIER AND THE  EXPECTED TURN TO THE WEST HAS
NOT MATERIALIZED AS OF YET... BOTH THE GLOBAL AND THE GFDL MODEL
DO NOT HAVE A WESTWARD MOVEMENT FOR ANOTHER 24 TO 36 HOURS.

1016 MB LOW PRESSURE LOCATED NEAR 28N65W ABOUT 200 MILES SSW OF
BERMUDA.  THE SYSTEM APPEARS TO BE GETTING A LITTLE BETTER
ORGANIZED. SATELLITE IMAGES INDICATE AN INCREASE IN CONVECTION
NEAR THE CENTER OF THE CIRCULATION... BUT THE  LOW-LEVEL CENTER
REMAINS W OF OF THE  MID-LEVEL CENTER LOCATED NEAR 29N67W.  THE
POTENTIAL FOR DEVELOPMENT IS POSSIBLE IN THE NEXT COUPLE OF
DAYS.  ISOLATED MODERATE FROM 28N-30N BETWEEN 64W-66W.

...TROPICAL WAVES...
TROPICAL WAVE ABOUT 280NM WEST OF THE CAPE VERDE ISLANDS ALONG
29W S OF 22N MOVING W 10-15 KT.  LONG-TERM SATELLITE LOOPS SHOW
A HIGH AMPLITUDE WAVE WITH INCREASING LOW/MID CLOUDS BEHIND THE
WAVE AXIS BUT NO SIGNIFICANT CONVECTION.

TROPICAL WAVE OVER THE CENTRAL CARIBBEAN ALONG 79W/808W S OF 17N
MOVING W 15-20 KT.  THIS WAVE REMAINS POORLY DEFINED IN
SATELLITE IMAGERY AND THE POSITION IS BASED ON EXTRAPOLATION.
SCATTERED MODERATE CONVECTION IS NOTED FROM PANAMA NOT TO
HONDURAS

...ITCZ...
ITCZ AXIS IS ALONG 10N15W 6N30W 13N40W 9N60W.  ISOLATED MODERATE
FROM 8N-13N BETWEEN 12W-20W AND FROM 031N-08N 24W-37W.

...DISCUSSION...
GULF OF MEXICO...
LITTLE CHANGES OVER THE LAST COUPLE OF DAYS...MID/UPPER LEVEL
RIDGE REMAINING OVER THE NW PORTION OF THE GULF EXTENDING FROM
SE TEXAS NEWD OVER SE LOUISIANA.  THE RIDGE IS BEING UNDERCUT BY
A RETROGRADING UPPER LOW ALONG THE S COAST OF MEXICO NEAR
CULIACAN.  CONFLUENCE BETWEEN THESE TWO FEATURES CONTINUES TO
PRODUCE LARGE SCALE SUBSIDENCE/DRY AIR ACROSS A MAJORITY OF THE
AREA.  THE SUBTROPICAL RIDGE WITH GENERALLY LIGHT SE FLOW ACROSS
REMAINS OVER THE AREA. UPPER RIDGE CONTINUES TO NUDGING INTO THE
SE GULF... WITH DRY AIR/SUBSIDENCE KEEPS THINGS MOSTLY DRY OVER
WATER.

CARIBBEAN SEA...
MID-OCEANIC TROUGH EXTENDS FROM THE CENTRAL ATLC ACROSS THE N
CARIBBEAN FROM HISPANIOLA TO THE E TIP OF THE YUCATAN
PENINSULA.  SUBSIDENCE/ DRY AIR ALONG AND N OF THE TROUGH
CONTINUES TO COVER ALL OF CUBA AND THE EXTREME NW CARIBBEAN
INCLUDING JAMAICA AND THE CAYMAN ISLANDS.  FURTHER S...A
WELL-DEFINED MID/UPPER LEVEL RIDGE EXTENDS FROM THE NW COLUMBIA
TO 17N85W SE OF THE YUCATAN PENINSULA.  THE RIDGE REMAINS NEARLY
STATIONARY ALLOWING AN AREA OF DISSIPATING ISOLATED MODERATE
CONVECTION TO PERSIST WITHIN 45 NM OF A LINE OVER CENTRAL
NICARAGUA AND PANAMA. ELSEWHERE...  WIDELY SCATTERED MODERATE
CONVECTION OVER THE SOUTH WEST PORT OF CUBA AND HAITI.

SUBTROPICAL ATLANTIC OCEAN...
TWO SURFACE LOWS HAVE FORMED FROM AN OLD FRONTAL BOUNDARY OVER
THE NW ATLC... ONE OF WHICH IS CURRENTLY TD 7.  THE DEPRESSION
HAS GENERALLY ENCOUNTERING LIGHT SHEAR... BEING UNDER THE
NORTHERN FLANK OF A RIDGE EXTENDING FROM THE NW BAHAMAS TO NE S
CAROLINA.  SECOND AREA OF LOW PRESSURE IS ABOUT 200 MILES SSW OF
BERMUDA BUT AND IS BEGINNING TO GET A BIT BETTER ORGANIZED.
SHEAR IS HIGHER OVER THE SECOND LOW WITH A NEARBY UPPER LOW
INHIBITING DEVELOPMENT.  ISOLATED SHOWERS ARE ALONG THE REMNANT
FRONTAL TROUGH N OF 24N BETWEEN 64W-72W.  MID/UPPER TROUGH ALONG
69W N OF 25N IS STATIONARY FOR NOW BUT FORECAST TO MOVE WESTWARD
AS UPPER HEIGHTS BUILD OVER THE MID-LATITUDE NW ATLC.  HOW MUCH
RIDGE IS BETWEEN THIS TROUGH AND FRANCES IN THE MEDIUM RANGE
SEEMS TO BE THE MAIN PLAYER IN DECIDING IF AND WHEN FRANCES WILL
TURN MORE NW AS IT APPROACHES THE GENERAL AREA NEAR THE BAHAMAS
IN 5 DAYS.  OVER THE CENTRAL ATLC... BROKEN MID-OCEANIC TROUGH
EXTENDS FROM 30N49W INTO THE CARIBBEAN OVER HISPANIOLA.  TROUGH
HAS BEEN WEAKENING WITH AN ANTICYCLONE FROM THE TROPICAL ATLC
SHIFTING NW-WARD.  THE E ATLC REMAINS UNDER MODERATE TO STRONG
SUBSIDENCE AND DRY/TRANQUIL WEATHER.  THE ONLY FEATURE OF NOTE
IS A MID-UPPER LEVEL TROUGH EXTENDING FROM BETWEEN THE AZORES
AND CANARY ISLANDS TO 25N38W. AT THE SURFACE.

TROPICAL ATLANTIC...
HURRICANE FRANCES CONTINUES TO BE THE MAIN WEATHER MAKER IN THE
DEEP TROPICS.   MID-UPPER RIDGE EXTENDING FROM AFRICA NEAR
MAURITANIA WSW TO 18N48W.   MODERATE SUBSIDENCE COVERS THE AREA
W OF THE LESSER ANTILLES. MODERATE SUBSIDENCE AND DRY AIR IS
ALSO PRESENT E OF FRANCES TO 30W TO THE CAPE VERDE ISLANDS.

$$
JP/RG



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