TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
159 PM EST FRI JAN 16 2009
 
LAST NO AMENDS...NEXT JAN 21.

DISCUSSION FROM JAN 16/0000 UTC. THE SYNOPTIC PATTERN SHOWS A
TROUGH ACROSS THE USA...WITH MEAN AXIS AT 500 HPA FORECAST TO
EXTEND SOUTH ACROSS THE EASTERN USA TO NORTH OF THE YUCATAN BY 24
HRS. ALTHOUGH MOST OF THE SHORT WAVE ENERGY QUICKLY SHEARS
EASTWARD...THIS WILL SET THE STAGE FOR ANOTHER TROUGH THAT RACES
ACROSS THE CENTRAL PLAINS TO THE EASTERN USA BY 72 HRS. THERE ARE
SOME DIFFERENCES AMONG THE GLOBAL AND REGIONAL MODELS ON THE
INTENSITY/SPEED OF THIS SYSTEM...SO WE ARE LIKELY TO SEE
CORRECTIONS/ ADJUSTMENTS TO THIS PATTERN IN THE NEXT FEW RUNS. THE
LOW LEVEL PATTERN CONTINUES TO SHOW A MEANDERING FRONT OVER THE
NORTHWEST BAHAMAS/WESTERN CUBA TO NORTHERN YUCATAN. ANOTHER FRONT
IS SURGING ACROSS FLORIDA AND THE GULF...DISPLACED BY A BUILDING
POLAR RIDGE OVER THE MIDWEST/EASTERN USA. THE BUILDING RIDGE WILL
DRIVE THE FRONT INTO THE NORTHWEST BAHAMAS-WESTERN CUBA EARLY THIS
PERIOD...WHERE IT WILL MERGE WITH THE OLD BOUNDARY. AS THE FRONTS
COMBINE...THEY WILL THEN CONTINUE ACROSS THE CENTRAL
BAHAMAS-CENTRAL/ WESTERN CUBA TO THE NORTHWEST CARIBBEAN BY 24-36
HRS. IT WILL THEN REMAIN NEARLY STATIONARY WHILE GRADUALLY
WEAKENING THROUGH 72-84 HRS. A NEW BOUNDARY MOVES ACROSS TEXAS TO
NORTHERN MEXICO BY 60 HRS...AND THROUGH 72/84 HRS IT WILL ADVANCE
TO THE NORTHERN GULF-NORTHEAST MEXICO. FRONTAL CONVECTION OVER THE
CENTRAL BAHAMAS AND OVER CENTRAL/WESTERN CUBA WILL RESULT IN
RAINFALL AMOUNTS OF 05-10MM/DAY AND ISOLATED MAXIMA OF 15MM. MOST
INTENSE EXPECTED THROUGH 36 HRS...AND DECREASING IN AREA
COVERAGE/INTENSITY THROUGH 60 HRS. 

IN ASSOCIATION WITH THESE FRONTS...MODEL ANALYSIS SHOWS A FRONTAL
SHEAR LINE THAT EXTENDS ACROSS THE SOUTHEAST BAHAMAS/EASTERN
CUBA-CAYMAN ISLES TO GULF OF HONDURAS/ SOUTHERN BELIZE-CENTRAL
GUATEMALA. THROUGH 24-30 HRS IT WILL MOVE TO FAR EASTERN
CUBA-JAMAICA TO NORTHEAST NICARAGUA. AT 36-48 HRS IT WILL DRIFTS
ACROSS HISPANIOLA TO COSTA RICA/WESTERN PANAMA...WHERE IT IS TO
REMAIN WHILE ALSO WEAKENING THROUGH 72-84 HRS. AN AREA OF DEEP
LAYERED MOISTURE LIES BETWEEN THE SURFACE FRONT TO THE NORTH AND
THE SHEAR LINE...WITH BOUNDARY LAYER MIXING RATIO VALUES RANGING
BETWEEN 16-18 G/KG OVER BELIZE-CENTRAL GUATEMALA-QUINTANA ROO AND
NORTHWEST HONDURAS. THIS...IN INTERACTION WITH THE DEEP POLAR
TROUGH OVER THE GULF OF MEXICO...WILL SUSTAIN ORGANIZED CONVECTION
ACROSS BELIZE/QUINTANA ROO-CENTRAL GUATEMALA AND NORTHWEST
HONDURAS. THE MOST INTENSE IS EXPECTED THROUGH 48-54 HRS. ON DAY
01 WE PROJECT RAINFALL AMOUNTS OF 15-30MM/DAY AND MAXIMA OF
40-80MM. ON DAY 02 IT WILL DECREASE TO 15-20MM/DAY AND MAXIMA OF
35-70MM...WHILE ON DAY 03 IT WILL PEAK AT 15-25MM. OTHER
CONVECTION IS EXPECTED OVER NORTHEAST HONDURAS AND NICARAGUA...BUT
IT IS NOT GOING TO BE AS INTENSE...WITH RAINFALL AMOUNTS OF
00-05MM/DAY AND MAXIMA OF 10MM. AS THE SHEAR LINE MEANDERS OVER
HISPANIOLA...IT WILL FAVOR RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 20-35MM ON DAY 02. ON DAY 03 THE MAXIMA WILL DECREASE TO
10-15MM/DAY. OVER THE CAYMAN ISLES THIS IS TO FAVOR ISOLATED
CONVECTION ON DAY 01...WHILE OVER JAMAICA IT WILL FAVOR SCATTERED
CONVECTION ON DAY 02 WITH MAXIMA OF 10-15MM. MOST INTENSE IS
EXPECTED ON THE CARIBBEAN PLAINS OF COSTA RICA TO WESTERN
PANAMA...WITH RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA OF
20-30MM.

THE STRONG LOW LEVEL RIDGE PATTERN OVER NORTH AMERICA SUSTAINS A
NORTHERLY WIND SURGE ACROSS THE GULF OF MEXICO. THIS IS INDUCING A
TEHUANTEPECER WIND THAT WILL REMAIN AT 30-40KT THROUGH 48-54
HRS...THEN RAPIDLY WANE. THE NORTHERLIES ARE ALSO CONVERGING
ACROSS EASTERN AND SOUTHERN MEXICO...FAVORING DENSE CLOUD COVER
AND OROGRAPHICALLY INDUCED CONVECTION. ACROSS SOUTHERN
TAMAULIPAS-VERACRUZ TO CHIAPAS-TABASCO/NORTHERN OAXACA THIS WILL
FAVOR RAINFALL AMOUNTS OF 15-25MM/DAY AND MAXIMA OF 35-70MM
THROUGH 36 HRS. THIS DECREASES TO 00-05MM/DAY AND ISOLATED MAXIMA
OF 10MM BY 36-60 HRS....WITH LESSER AMOUNTS LATER IN THE CYCLE.

THE BOUNDARY LAYER WINDS ARE ALSO SURGING ACROSS THE WESTERN
CARIBBEAN TO THE EASTERN PACIFIC. CROSS SECTIONAL ANALYSIS SHOWS A
GRADUAL INTENSIFICATION OF THE TRADE WIND INVERSION TO THE SOUTH
OF COSTA RICA/PANAMA BY 60-66 HRS...WHICH LEADS TO A SHARP
DECREASE IN PRECIPITABLE WATER CONTENT VALUES ALONG THE
CONVERGENCE ZONE. THIS IS TO HAVE AN IMPACT ON ITCZ RELATED
CONVECTION ACROSS THE ANDEAN REGION AND PACIFIC COASTAL PLAINS OF
COLOMBIA. ON AREA SOUTH OF 05N THE DAILY MAXIMA WILL PEAK AT
25-50MM/DAY THROUGH 48 HRS...WHILE NORTH OF 05N THE MAXIMA PEAKS
AT 20-40MM/DAY BY 36 HRS AND 15-30MM/DAY THEREAFTER. EVEN LOWER
AMOUNTS ARE QUITE POSSIBLE ON DAY 03.


UNDER INFLUENCE OF THE LONG WAVE TROUGH PATTERN OVER NORTH
AMERICA...THE SUBTROPICAL RIDGE OVER THE ATLANTIC RECEDED. AT 250
HPA A WEAK/OPEN RIDGE REMAINS OVER VENEZUELA/ EASTERN
CARIBBEAN...WHILE A STRONGER RIDGE ESTABLISHED OVER THE CENTRAL
ATLANTIC. THE LATTER CENTERS ON A HIGH AT 30N 40W...AND IT WILL
DRIFT TO 25N 30W BY 72 HRS. AT 500 HPA A HIGH NEAR 30N 40W ANCHORS
A RIDGE OVER THE CENTRAL/EASTERN ATLANTIC TO JUST EAST OF THE
ISLANDS. THE RIDGE SLOWLY BUILDS TO THE SOUTHWEST ACROSS THE
NORTHERN LEEWARD/VIRGIN ISLES BY THE END OF THE CYCLE. AS A
RESULT...THE TRADE WIND INVERSION IS FORECAST TO GRADUALLY
INTENSIFY AS THE CYCLE PROGRESSES. DEEP LAYER CONVECTIVE
INSTABILITY IS TO PERSIST OVER THE NORTHEAST CARIBBEAN ISLES
THROUGH AT LEAST 48-60 HRS. 

THERE IS ALSO A TUTT LOW NEAR 16N 55W...WHICH ANCHORS A SHORT WAVE
TROUGH OVER AND EAST OF THE LESSER ANTILLES/ NORTH OF THE GUIANAS.
THIS FEATURE IS CUTOFF FROM THE FLOW...AND AS A RESULT IS EXPECTED
TO WEAKEN WHILE SLOWLY PULLING TO THE EAST-NORTHEAST THROUGH 72
HRS. AT 500 HPA IT SUPPORTS A TROUGH OVER THE SOUTHEAST
CARIBBEAN-NORTHERN WINDWARD ISLES...WITH AN ILL ORGANIZED LOW
CENTERING NORTH OF THE ABC ISLES/LA GUAJIRA PENINSULA. THIS FAVORS
A MOIST SURGE ACROSS THE LEEWARD/VIRGIN ISLES TO PUERTO RICO AND
HISPANIOLA. BEST DYNAMICS/MOISTURE CONVERGENCE IS FORECAST ACROSS
THE LEEWARD/VIRGIN ISLES INTO PUERTO RICO THROUGH 36-42
HRS...WHILE OVER THE DOMINICAN REPUBLIC THIS PERSISTS THROUGH
60-72 HRS. OVER THE LEEWARD ISLES WE EXPECT RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 20-35MM/DAY THROUGH 36-48 HRS...WHILE
OVER PUERTO RICO THE MAXIMA PEAKS AT 25-50MM. SIMILARLY OVER
HISPANIOLA...WITH MAXIMA OF 25-50MM THROUGH 36 HRS...20-35MM/DAY
AT 36-60 HRS...AND 10-15MM/DAY AT 60-72 HRS. OTHER CONVECTION IS
EXPECTED FARTHER SOUTH ALONG THE NORTHERN COAST OF VENEZUELA TO
THE ABC ISLANDS...WHERE WE EXPECT RAINFALL AMOUNTS OF 00-05MM/
DAY...WITH MAXIMA OF 10MM TO CONCENTRATE OVER LAKE MARACAIBO
REGION. ON THE BASE OF THE TUTT...IN INTERACTION WITH THE ATLANTIC
ITCZ...WE EXPECT SOME CONVECTIVE ENHANCEMENT FROM NORTHEAST
VENEZUELA TO NORTHERN GUYANA/ SURINAME...WITH RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15-25MM. THIS ACTIVITY IS TO SURGE
ACROSS TRINIDAD TO THE GRENADINES BY 30-54 HRS. 

ARANDA....ETESA (PANAMA) 
JIMENEZ...FAC (COLOMBIA)
DAVISON...NCEP (USA)