939
FXCA20 KWBC 211929
PMDCA
TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
229 PM EST FRI NOV 21 2008
DISCUSSION FROM NOV 21/0000 UTC. THE GLOBAL AND REGIONAL MODELS
INITIALIZE A BROAD TROUGH PATTERN NORTH OF THE ISLANDS. EMBEDDED
IN THIS FLOW...AT MID LEVELS...A PROGRESSIVE CLIPPER LOW WILL MOVE
ACROSS THE MID ATLANTIC REGION OF THE USA EARLY THIS CYCLE...TO
THEN LIFT TO THE NORTHEAST. ANOTHER EJECT ACROSS THE EASTERN USA
BY 60 HRS...AND AMPLIFIES TO JUST NORTH OF THE ISLANDS ALONG 70W
BY 72 HRS. AT LOW LEVELS...A SURFACE FRONT EXTENDS ACROSS NORTHERN
HISPANIOLA TO THE NORTHWEST CARIBBEAN. THE FRONT MEANDERS TO THE
SOUTHEAST BAHAMAS/TURKS-EASTERN CUBA EARLY THIS PERIOD. THE
TRAILING END OVER THE WESTERN CARIBBEAN... HOWEVER...IS TO WEAKEN.
THE BOUNDARY WILL THEN WEAKEN/ DISSIPATE THROUGH 42-48 HRS AS A
NEW FRONT MOVES ACROSS THE BAHAMAS. AS THE FRONT RETROGRESSES
EXPECT LIGHT CONVECTION OVER THE SOUTHEAST BAHAMAS/TURKS AND
EASTERN CUBA. OVER HISPANIOLA...MEANWHILE...EXPECT RAINFALL
AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 30-60MM/DAY. ALTHOUGH THE
FRONT RETROGRESSES...THE RAINS WILL PERSIST OVER THE ISLAND UNDER
INFLUENCE OF A MEANDERING SHEAR LINE.
MODELS CONTINUE TO FORECAST A NEW FRONT TO ENTER THE NORTHWEST
BAHAMAS-SOUTHERN FLORIDA THROUGH 24-30 HRS. THROUGH 42-48 HRS IT
WILL MOVE TO THE CENTRAL BAHAMAS-NORTHWEST CUBA/STRAITS OF FLORIDA
TO THE NORTHWEST GULF OF MEXICO. AT 60-72 HRS IT WILL MOVE TO
SOUTHEAST BAHAMAS/ TURKS...MEANDERING ACROSS CENTRAL/WESTERN CUBA
TO THE GULF OF MEXICO. IT WILL THEN REMAIN NEARLY STATIONARY
THROUGH 84 HRS. AS IT MOVES ACROSS THE NORTHWEST/CENTRAL BAHAMAS
AND CUBA IT WILL FAVOR WIDELY ISOLATED CONVECTION...AND RAINFALL
AMOUNTS OF 00-05MM/DAY AND MAXIMA OF 10MM. OVER THE SOUTHEAST
BAHAMAS AND THE TURKS... HOWEVER...HIGHER AMOUNTS ARE EXPECTED
WITH ACCUMULATION OF 05-10MM/DAY AND MAXIMA OF 15-25MM.
BEHIND THIS FRONT...AT LOW LEVELS...A POLAR RIDGE WILL MOVE TO THE
LOWER MISSISSIPPI VALLEY IN THE USA EARLY IN THE CYCLE. BUT
THROUGH 42-48 HRS IT WILL RELOCATE TO THE SOUTHEAST USA WHILE THE
RIDGE BUILDS TO THE EAST INTO THE WESTERN ATLANTIC. EARLY IN THE
CYCLE...THE POLAR RIDGE IS TO BRIEFLY STRENGTHEN THE LOW LEVEL
NORTHERLIES ACROSS THE GULF OF MEXICO AND THE WESTERN CARIBBEAN.
BUT AS THE RIDGE MOVES TO THE EAST...THE WINDS ACROSS THE GULF OF
MEXICO WILL TAKE AN EASTERLY COMPONENT BY MID CYCLE. THE WINDS
ACROSS CUBA TO CENTRAL AMERICA WILL REMAIN FROM THE
NORTH-NORTHEAST DURING THE CYCLE. OVER THE GULF...THE WINDS WILL
RANGE FROM 10-20KT...WHILE OVER THE WESTERN CARIBBEAN/ NORTHERN
CENTRAL AMERICA THEY WILL PEAK AT 25-30KT. THE NORTHERLIES WILL
CONVERGE ACROSS NORTHERN HONDURAS INTO CENTRAL GUATEMALA...WHERE
OROGRAPHICALLY INDUCED CONVECTION WILL RESULT IN RAINFALL AMOUNTS
OF 05-10MM/DAY AND MAXIMA OF 20-40MM/DAY. THIS IS TO GRADUALLY
DECREASE TO ISOLATED MAXIMA OF 15-30MM/DAY BY 72-84 HRS. OVER
MEXICO...AS THE WINDS SHIFTS TO THE EAST...THE LOW LEVEL MOISTURE
CONVERGENCE IS TO ALSO SHIFT NORTH FROM OAXACA-VERACRUZ TO
TAMAULIPAS-NUEVO LEON-NORTHERN VERACRUZ THROUGH 36-48 HRS...WITH
RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 15-20MM.
SURFACE ANALYSIS SHOWS AN AREA OF MOISTURE CONVERGENCE THAT
EXTENDS FROM THE DOMINICAN REPUBLIC TO A LOW OVER CENTRAL
PANAMA/SOUTHERN CARIBBEAN. ANALYSIS OF THE BOUNDARY LAYER
ISODROSOTHERMS GRADIENT AND THE STREAM LINE ANALYSIS SUGGESTS THAT
THIS IS A SHEAR LINE AND NOT A FRONT...AND THIS CORRELATES QUITE
WELL WITH WHAT THE GLOBAL MODELS FORECAST. THIS FEATURE REMAINS
NEARLY STATIONARY AS ANOTHER STARTS TO MOVE ACROSS CUBA TO THE
GULF OF HONDURAS EARLY IN THE CYCLE. THROUGH 24 HRS IT IS TO
CONTINUE ACROSS THE SOUTHEAST BAHAMAS/TURKS-WINDWARD PASSAGE OF
CUBA TO COSTA RICA/WESTERN PANAMA. AT 36 HRS...DISPLACED BY THE
BUILDING POLAR RIDGE...IT WILL MOVE TO PUERTO RICO-COSTA
RICA...AND IT WILL CONTINUE THROUGH THE VIRGIN ISLES THROUGH 48-60
HRS. AT 72-84 HRS THE SHEAR LINE WILL REACH THE FRENCH/ LEEWARD
ISLANDS...TRAILING ALONG THE COAST OF VENEZUELA TO THE SOUTHERN
CARIBBEAN. THE EVALUATION OF THE FORECASTED PRECIPITABLE WATER
CONTENT SHOW HIGH VALUES ACROSS SOUTHERN CENTRAL AMERICA/SOUTHERN
CARIBBEAN INTO NORTHERN SOUTH AMERICA DURING THE NEXT 60
HRS...WITH A DECREASE TO THE NORTH OF 15N TOWARDS THE END OF THE
CYCLE...WITH A SHARP DECREASE OVER THE FRENCH AND LEEWARD ISLANDS
BY 72 HRS. AS THE SHEAR LINE ENTERS THE WESTERN CARIBBEAN...WE
EXPECT CONVECTION OVER NORTHERN HONDURAS TO PEAK AT 20-40MM/DAY...
TO DECREASE TO 20-35MM LATER IN THE CYCLE. OVER SOUTHERN NICARAGUA
TO COSTA RICA/WESTERN PANAMA THE MODELS CONTINUE TO FORECAST
MODERATE TO HEAVY RAINFALL AMOUNTS. A SURGE IN ACTIVITY IS NOW
EXPECTED WITH THE ARRIVAL OF THE SHEAR LINE...WITH RAINFALL
AMOUNTS TO INCREASE AGAIN TO 30-60MM/DAY AND MAXIMA OF 75-125MM.
ON DAY 03 WE EXPECT A GRADUAL DECREASE TO RAINFALL AMOUNTS OF
20-35MM/DAY AND MAXIMA OF 40-80MM... WITH AREA OF ORGANIZED
CONVECTION LIFTING NORTH OF PANAMA/COSTA RICA AND EXPANDING ACROSS
EASTERN NICARAGUA. ACROSS HISPANIOLA TO PUERTO RICO WE ONLY
FORESEE RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 20-35MM/DAY
THROUGH 48-60 HRS...WHILE OVER THE NORTHERN LEEWARD-VIRGIN ISLES
ONLY EXPECT ISOLATED CONVECTION.
AS THE UPPER LEVEL TROUGH MEANDERS OVER THE EASTERN USA/ WESTERN
ATLANTIC...THE SUBTROPICAL RIDGE TO THE SOUTH WILL LIMIT TO
NORTHERN SOUTH AMERICA/CARIBBEAN-CENTRAL AMERICA TO THE EASTERN
TROPICAL PACIFIC. THIS WILL REMAIN NEARLY UNCHANGED THROUGH 48-60
HRS...BUT BY 72 HRS IT WILL BUILD ACROSS MEXICO/THE GULF TO THE
CENTRAL USA...WHILE OVER THE CARIBBEAN IT WILL REMAIN RELATIVELY
FLAT. AS IT MEANDERS ACROSS THE CARIBBEAN THE RIDGE WILL
PROVIDE/SUSTAIN THE VENTILATION ALOFT IN SUPPORT OF DEEP
CONVECTION ALONG THE ITCZ/NEAR EQUATORIAL TROUGH. THE CONVERGENCE
ZONE REMAINS NORTH OF ITS CLIMATOLOGICAL POSITION. THIS WILL FAVOR
HEAVY RAINS FROM NORTHERN COLOMBIA/VENEZUELA INTO THE ABC
ISLES...AND ALSO EAST INTO THE WINDWARD AND SOUTHERN FRENCH
ISLANDS. MOST INTENSE OVER THE SOUTHEAST CARIBBEAN ISLES IS
EXPECTED THROUGH 42-48 HRS...WHILE OVER NORTHERN COLOMBIA/
NORTHWEST VENEZUELA AND THE ABC ISLES THIS IS TO GENERALLY PERSIST
THROUGH 72-84 HRS. OVER THE FRENCH/WINDWARD ISLES MAXIMA WILL PEAK
AT 25-50MM THROUGH 36 HRS...AND 20-35MM AT 36-60 HRS. OVER THE ABC
ISLES/NORTHWEST VENEZUELA TO NORTHERN COLOMBIA MAXIMA WILL PEAK AT
40-80MM BY 24-48 HRS... WITH MAXIMA TO DECREASE TO 30-60MM AT
36-60 HRS... AND 20-30MM/DAY AT 60-84 HRS. ALSO NOTE THAT BETWEEN
DAYS 02 AND 03...AS THE SHEAR LINE SETTLES OVER NORTHERN
VENEZUELA...THE MODELS INITIALLY SHOW A SURGE BETWEEN FALCON AND
CARACAS...WITH A SHARP DECREASE LATER IN THE CYCLE.
PERTURBATIONS IN THE EASTERLIES.
INIT F24 F36 F48 F60 F72 F84
49W 52W 55W 57W 59W DISSIPATES
66W 67W 69W 71W 72W 75W 77W
THE WAVE ALONG 49W IS TO PROPAGATE ALONG THE ITCZ AS IT MEANDERS
ALONG 10N. AS A RESULT...IT IS NOT TO AFFECT THE GUIANAS.
THE PERTURBATION ALONG 66W WILL MOVE ALONG THE EQUATORIAL TROUGH
AS IT MEANDERS ACROSS NORTHERN SOUTH AMERICA...WHERE IT WILL
ENHANCE CONVECTION TO RESULT IN RAINFALL MAXIMA OF 40-80MM/DAY
OVER NORTHWESTERN VENEZUELA/LA GUAJIRA PENINSULA.
GREENE...DM (BAHAMAS)
ARANDA...ETESA (PANAMA)
DAVISON...NCEP (USA)
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page