[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 280555
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
205 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 0000 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
0545 UTC.

...SPECIAL FEATURES...
TROPICAL DEPRESSION SEVEN IS CENTERED NEAR 31.3N 78.0W AT
28/0300 UTC WITH MAXIMUM SUSTAINED WINDS OF 25 KT GUSTING TO 35
KT.  ESTIMATED MINIMUM CENTRAL PRESSURE IS 1012 MB WITH THE
DEPRESSION DRIFTING SSE. SEE THE LATEST NHC PUBLIC ADVISORY OR
FORECAST/ADVISORY ISSUED UNDER AWIPS/WMO HEADERS MIATCPAT2/
WTNT32 KNHC OR MIATCMAT2/ WTNT22 KNHC FOR MORE DETAILS. THE
CIRCULATION CENTER IS NOT WELL DEFINED ON SATELLITE IMAGERY.
CLOUD PATTERN IS RATHER SYMMETRIC WITH SOME BANDING BUT STILL
REMAINS UNORGANIZED.  SOME STRENGTHENING IS FORECASTED IN THE
NEXT 36 HOURS.

HURRICANE FRANCES IS CENTERED NEAR 16.6N 50.5W AT 28/0300 UTC
MOVING NW 10 KT.  MAXIMUM SUSTAINED WINDS OF 100 KT WITH GUSTS
TO 120 KT MAKING FRANCES THE 3RD MAJOR HURRICANE OF 2004.
ESTIMATED MINIMUM CENTRAL PRESSURE IS 962 MB.  SEE THE LATEST
NHC FORECAST/ADVISORY ISSUED UNDER AWIPS/ WMO HEADERS
MIATCMAT1/WTNT21 KNHC FOR MORE DETAILS.   BASED UPON SSMI IMAGES
AND INFRARED SATELLITE ANIMATION...FRANCES APPEARS TO HAVE GONE
THROUGH AN EYEWALL REPLACEMENT CYCLE WITH THE NET RESULT BEING A
LARGE EYE DIAMETER AND LIKELY DECREASE IN WIND SPEED...BUT
INTENSIFICATION IS EXPECTED.  SWELL FROM THE HURRICANE IS
EXPECTED TO REACH THE LESSER ANTILLES THIS MORNING AND PUERTO
RICO BY SUN.  SCATTERED STRONG CONVECTION WITHIN 90 NM OF THE
CENTER.

1016 MB LOW PRESSURE LOCATED NEAR 29N66W ABOUT 200 MILES SSW OF
BERMUDA.  THE SYSTEM APPEARS TO BE MISALIGNED WITH THE LOW-LEVEL
CENTER W OF A MID-LEVEL CENTER LOCATED NEAR  29N67W.   THERE IS
LITTLE CONVECTION ASSOCIATED WITH THE SYSTEM...  BUT THE
POTENTIAL FOR DEVELOPMENT IS POSSIBLE IN THE NEXT COUPLE OF
DAYS.  ISOLATED MODERATE FROM 28N-30N BETWEEN 64W-66W.

...TROPICAL WAVES...
TROPICAL WAVE 200NM WEST OF THE CAPE VERDE ISLANDS ALONG 28W 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 77W/78W S OF 17N
MOVING W 15-20 KT.  THIS WAVE REMAINS POORLY DEFINED IN
SATELLITE IMAGERY AND THE POSITION IS BASED ON EXTRAPOLATION.

...ITCZ...
ITCZ AXIS IS ALONG 10N15W 6N30W 13N40W 9N60W.  ISOLATED MODERATE
CONVECTION ALONG THE ITCZ WITH IN 60 NM OF AXIS.

...DISCUSSION...
GULF OF MEXICO...
THERE HAS BEEN 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 TO THE NW FLORIDA
PANHANDLE.  THE RIDGE IS BEING UNDERCUT BY A RETROGRADING UPPER
LOW ALONG THE S COAST OF MEXICO NEAR ACAPULCO.  CONFLUENCE
BETWEEN THESE TWO FEATURES CONTINUES TO PRODUCE LARGE SCALE
SUBSIDENCE/DRY AIR ACROSS A MAJORITY OF THE AREA. AT THE
SURFACE...THE REMNANT FRONTAL TROUGH CONTINUES TO SLOWLY
DISSIPATING AND REMAINS OVER THE CENTRAL GULF OF MEXICO FROM
29N89W WSW TO 26N96W.  THE SUBTROPICAL RIDGE WITH GENERALLY
LIGHT SE FLOW ACROSS 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.

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 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
REMAINS LESS ORGANIZED THAN TD 7.  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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