[Tropical] Tropical Weather Discussion

[Nashville EMWIN]

AXNT20 KNHC 280002
TWDAT

TROPICAL WEATHER DISCUSSION
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
805 PM EDT FRI 27 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 1800 UTC SURFACE ANALYSIS AND SATELLITE IMAGERY THROUGH
2315 UTC.

...SPECIAL FEATURES...
LOW 150 MILES SE OF CHARLESTON S CAROLINA IS NOW TROPICAL
DEPRESSION SEVEN.  IT IS LOCATED NEAR 31.3N 77.3W AT 28/0000 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.  AN AREA
OF TSTMS HAS COALESCED NEAR THE CENTER OF A BROAD CIRCULATION
WITH AN IMPRESSIVE PATTERN ON LATE VISIBLE SATELLITE PICTURES.
THE SYSTEM HAS A SMALL WIND FIELD AS INDICATED BY NEARBY BUOYS
BUT SHOULD HAVE A CHANCE TO INCREASE STRENGTH WITH ANTICYCLONIC
UPPER FLOW AND LIGHT SHEAR PLUS WARM WATERS NEARBY.  WIDELY
SCATTERED MODERATE FROM 30N-32N BETWEEN 76W-79W.

HURRICANE FRANCES IS CENTERED NEAR 15.7N 49.8W AT 27/2100 UTC
MOVING NW 10 KT.  MAXIMUM SUSTAINED WINDS CONTINUE TO INCREASE,
NOW UP TO 100 KT WITH GUSTS TO 115 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.
FRANCES BECOMES THE 3RD MAJOR HURRICANE TO FORM IN AUGUST... THE
FIRST TIME THAT HAS HAPPENED SINCE 1950.  IN ADDITION... THIS IS
THE EARLIEST THAT THE THIRD MAJOR HURRICANE OF THE YEAR HAS
FORMED SINCE 1916. THE EYE OF FRANCES HAS BECOME MORE WELL-
DEFINED OVER THE PAST 6 HOURS AND IS EMBEDDED SLIGHTLY W OF THE
CENTER OF THE CENTRAL DENSE OVERCAST (CDO).  CIRRUS OUTFLOW IS
FANNING OUT EVERYWHERE ESPECIALLY TO THE N.  SWELL FROM THE
HURRICANE IS EXPECTED TO REACH THE LESSER ANTILLES SAT INTO
PUERTO RICO BY SUN.  SCATTERED STRONG WITHIN 90 NM OF THE CENTER.

1016 MB LOW PRESSURE LOCATED NEAR 29N65W ABOUT 250 MILES SSW OF
BERMUDA.  THE SYSTEM APPEARS TO BE MISALIGNED WITH THE LOW-LEVEL
CENTER W OF A MID-LEVEL CENTER SEEN ABOUT 29N63.5W.  AN UPPER
LOW NEAR 29N68W MAY HINDER THE DEVELOPMENT OF THIS SYSTEM BUT
THE SURFACE LOW HAS THE POTENTIAL TO BECOME A TROPICAL CYCLONE
IN THE NEXT COUPLE OF DAYS.  ISOLATED MODERATE FROM 27N-30N
BETWEEN 62W-66W.

...TROPICAL WAVES...
TROPICAL WAVE JUST WEST OF THE CAPE VERDE ISLANDS ALONG 27W 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 76W/77W 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 15N15W 7N30W 11N40W 7N59W.  ISOLATED MODERATE
WITHIN 45 NM OF AXIS W OF 56W.  SCATTERED MODERATE WITHIN 60 NM
OF 7N33W.

...DISCUSSION...
GULF OF MEXICO...
SMALL CHANGES SINCE YESTERDAY WITH A 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 SAVE THE NE GLFMEX WHERE A SMALL
UPPER LOW IS JUST W OF JACKSONVILLE PRODUCING WIDELY SCATTERED
TSTMS OVER FLORIDA N OF LAKE OKEECHOBEE E OF CEDAR KEY. AT THE
SURFACE...REMNANT FRONTAL TROUGH FROM N FLORIDA TO 26N94W IS
DISRUPTING THE SUBTROPICAL RIDGE WITH GENERALLY LIGHT SE FLOW
ACROSS THE AREA.   UPPER RIDGE IS 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 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 HAS BEEN NEARLY STATIONARY DURING
THE LAST 24 HOURS ALLOWING AN AREA OF DISSIPATING ISOLATED
MODERATE CONVECTION TO PERSIST WITHIN 45 NM OF A LINE FROM
10N80W TO CENTRAL NICARAGUA NEAR 12.5N84W.  HOWEVER...NUMERICAL
GUIDANCE INDICATES THE RIDGE WILL BEGIN RETREATING SLOWLY WEST
DURING THE NEXT 12-24 HOURS ALLOWING THE AREA OF CONVECTION TO
MOVE INTO CENTRAL AMERICA.

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 250 MILES SSW OF BERMUDA BUT IS
LESS ORGANIZED THAN THE WESTERN SYSTEM.  SHEAR IS HIGHER OVER
THE SECOND LOW WITH A NEARBY UPPER LOW INHIBITING DEVELOPMENT.
ISOLATED SHOWERS ARE ALONG THE REMNANT FRONTAL TROUGH N OF 25N
BETWEEN 65W-72W.  MID/UPPER TROUGH ALONG 68W 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...SUBTROPICAL RIDGE
IS WEAK W OF 50W WITH WEAKER THAN AVERAGE WINDS OVER MOST OF THE
SUBTROPICAL ATLC EXCEPT CLOSE TO AFRICA.  RIDGE AXIS IS MORE
PRONOUNCED OVER THE E ATLC FROM THE AZORES TO 29N49W.

TROPICAL ATLANTIC...
HURRICANE FRANCES IS OBVIOUSLY THE MAIN STORY IN THE DEEP
TROPICS ON THE SW FLANK OF AN UPPER ANTICYCLONE NEAR 18N42W
RIDGING W ... N OF THE CYCLONE TO 17N55W.   WEAK TROUGHING IS
PRESENT W OF 56W WITH PLENTY OF DRY AIR/SUBSIDENCE.  THE
HURRICANE IS HEADED TOWARD THIS BREAK IN THE RIDGE... THOUGH
MODELS AT VARIOUS SPEEDS REBUILD THE RIDGE AND TURN THE SYSTEM
MORE WESTWARD AFTER A DAY OR TWO.  THE QUESTION OF COURSE IS HOW
SHARP OF A TURN AND HOW SOON IT WILL OCCUR WHICH HAS LONG-TERM
IMPLICATIONS FOR THE FUTURE PATH OF FRANCES. IN ANY EVENT LARGE
SWELL WILL BE AFFECTING THE LESSER ANTILLES SAT INTO PUERTO RICO
WATERS BY SUN.  FARTHER E... MID-UPPER RIDGE CONTINUES ENE TO NW
SAHARA WITH MODERATE SUBSIDENCE AND MIDDLE TO UPPER LEVEL DRY E
OF FRANCES TO 30W.

$$
BLAKE

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