TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
231 PM EDT MON SEP 15 2008
 
DISCUSSION FROM SEP 15/0000 UTC. A BROAD POLAR TROUGH MOVES ACROSS
THE CENTRAL TO EASTERN USA OVER THE NEXT 36-48 HRS...WITH AXIS TO
REACH EASTERN SEABOARD BY 48-60 HRS. THE BASE OF THE
TROUGH...HOWEVER...IS TO TRAIL ALONG THE NORTHERN GULF TO TEXAS.
THIS TROUGH SUPPORTS A FRONT OVER SOUTHEAST LOUISIANA-NORTHWEST
GULF/SOUTHERN TEXAS TO TAMAULIPAS/COAHUILA. THROUGH 24 HRS THE
FRONT MOVES ACROSS ALABAMA...TRAILING TO NORTHERN TAMAULIPAS. BY
36-48 HRS THE FRONT MOVES TO GEORGIA/NORTHERN FLORIDA...WHILE
TRAILING ACROSS THE GULF TO SOUTHERN TAMAULIPAS/NORTHERN VERACRUZ.
A WAVE/LOW FORMS ALONG THE TAIL END OF THE FRONT OVER THE
NORTHWEST GULF BY 36-54 HRS...WHICH HELPS SUSTAIN A MEANDERING
FRONT ACROSS NORTHEAST MEXICO THROUGH 72-84 HRS. THE GENERAL
TENDENCY...HOWEVER...IS FOR THE FRONT TO START WEAKENING LATER IN
THE CYCLE. THIS FEATURE WILL SUSTAIN ORGANIZED DEEP CONVECTION
ACROSS NORTHEAST MEXICO...TO FIRST AFFECT COAHUILA/NUEVO LEON WITH
ACCUMULATION OF 10-15MM/DAY AND MAXIMA OF 30-60MM/DAY. THIS IS TO
QUICKLY BUILD ACROSS TAMAULIPAS...WHERE IT WILL SUSTAIN RAINFALL
AMOUNTS OF 10-15MM/DAY AND MAXIMA OF 30-60MM. MOST INTENSE IS
EXPECTED THROUGH 36-48 HRS. 

FURTHERMORE...A PREFRONTAL SHEAR LINE IS TO MOVE ACROSS TAMAULIPAS
MEXICO BY 24 HRS...INTO VERACRUZ BY 36 HRS. THIS ADVANCES TO
SOUTHERN VERACRUZ/NORTHERN OAXACA BY 48 HRS...TO THEN MEANDER OVER
OAXACA-TABASCO THROUGH 72-84 HRS. AS THE FRONT
WEAKENS...HOWEVER...THE SHEAR LINE IS ALSO FORECAST TO GRADUALLY
WEAKEN BY THE END OF THE CYCLE. THIS FEATURE WILL SUSTAIN BOUNDARY
LAYER WINDS OF 20-25KT...WHICH WHEN COUPLED WITH HIGH MIXING RATIO
VALUES WILL ALLOW FOR HEAVY TOPOGRAPHICALLY INDUCED CONVECTION TO
AFFECT THE CENTRAL-SOUTHERN STATES OF MEXICO. AT 24-36 HRS
CONVECTION WILL CONCENTRATE OVER TAMAULIPAS-SAN LUIS POTOSI WITH
ACCUMULATION OF 15-25MM/DAY AND MAXIMA OF 40-80MM. BY 48-60 HRS
HEAVY CONVECTION WILL AFFECT VERACRUZ-PUEBLA-OAXACA-TABASCO AND
POSSIBLY NORTHERN CHIAPAS...WITH MAXIMA OF 40-80MM. AT 72-84 HRS
MAXIMA WILL DECREASE TO 30-60MM... WHILE CONCENTRATING ACROSS
TABASCO-CHIAPAS/NORTHERN OAXACA.

VENTING DEEP CONVECTION...THE MODEL ANALYSIS/FORECAST SHOWS A CELL
OF THE SUBTROPICAL RIDGE OVER CENTRAL/NORTHERN MEXICO. ANOTHER
CELL EXTENDS OVER THE WESTERN CARIBBEAN/ CENTRAL AMERICA. A TUTT
OVER THE GULF SEPARATES THESE RIDGES...AS IT EXTENDS ALONG 80W TO
SOUTHERN MEXICO. AS THE MID/UPPER LEVEL POLAR TROUGH MOVES ACROSS
THE USA IT WILL INTERACT WITH THIS TUTT...FORCING MOST OF THE
SHORT WAVE ENERGY TO GRADUALLY SHEAR/LIFT TO THE NORTHEAST. BY 48
HRS A SHORT WAVE TROUGH IS ALL THAT REMAINS ALONG 87W/88W... WITH
WEAK VORTEX INTO WESTERN CUBA BY 72 HRS. THE DEEP TUTT IS HAVING
AN IMPACT ON ORGANIZED CONVECTION OVER THE CENTRAL
CARIBBEAN/CENTRAL AMERICA...WHERE IT IS INTERACTING WITH A
TROPICAL WAVE IN SUPPORT OF HEAVY CONVECTION. PLEASE SEE BELOW FOR
DETAILS. ACROSS CUBA...THIS TROUGH WILL FAVOR A GRADUAL INCREASE
IN CONVECTION AS IT FAVORABLY INTERACTS WITH SEA BREEZE
CONVERGENCE...TO RESULT IN RAINFALL AMOUNTS OF 05-10MM/DAY AND
MAXIMA OF 15-20MM. SIMILARLY ACROSS THE NORTHWEST BAHAMAS BY THE
END OF THE CYCLE.

ANOTHER CELL OF THE SUBTROPICAL RIDGE CENTERS OVER THE WESTERN
ATLANTIC/NORTH OF THE GREATER ANTILLES...WITH 250 HPA HIGH TO
MEANDER NEAR 32N 70W THROUGH 48-60 HRS. THIS RIDGE...AS IT
MEANDERS OVER THE WESTERN ATLANTIC...IS TO INITIALLY SLOW DOWN THE
EASTWARD PROGRESSION OF THE POLAR TROUGH OVER NORTH AMERICA. BUT
BY THE END OF THE CYCLE IT IS TO NEARLY COLLAPSE UNDER THE
INFLUENCE OF THIS PERTURBATION. MEANWHILE...THIS TROUGH WILL
SUPPORT THE INFLOW OF COLD POLAR ENERGY INTO THE BACKSIDE OF A
DEEPENING TROUGH OVER THE CENTRAL ATLANTIC...WITH TROUGH AXIS TO
EXTEND AT 250 HPA BETWEEN 55W/63W TO THE NORTHEAST CARIBBEAN. THIS
TROUGH MOVES WEST ALONG 70W TO NORTHWEST VENEZUELA/NORTHERN
COLOMBIA BY 48 HRS. AT 72 HRS IT WILL SPLIT IN TWO...WITH A VORTEX
TO THE NORTH TO SLOWLY LIFT TO THE NORTHEAST...WHILE ONE TO THE
SOUTH MEANDERS OVER HISPANIOLA. THIS TROUGH SUPPORTS AN INDUCED
TROUGH IN THE LOW LEVEL EASTERLIES (SEE BELOW FOR WAVE AXIS). OVER
THE NORTHERN LEEWARD-VIRGIN ISLES...PUERTO RICO AND HISPANIOLA
THIS FEATURE WILL INTERACT WITH SEA BREEZE CONVERGENCE TO RESULT
IN RAINFALL AMOUNTS OF 05-10MM/DAY AND MAXIMA OF 20-35MM. THIS IS
TO PERSIST THROUGH 60-72 HRS. SIMILAR AMOUNTS ARE EXPECTED OVER
NORTHERN GUYANA-NORTHEAST VENEZUELA AND SOUTHERN WINDWARD ISLES
(TRINIDAD-TOBAGO-GRENADINES). MOST INTENSE
CONVECTION...HOWEVER...IS EXPECTED ACROSS CENTRAL TO NORTHWEST
VENEZUELA EARLY IN THE PERIOD...AS THE UPPER TROUGH INTERACTS WITH
THE ITCZ/NET TO FAVOR RAINFALL AMOUNTS OF 10-15MM/DAY AND MAXIMA
OF 25-50MM. THIS GRADUALLY BUILDS WEST INTO THE EASTERN PLAINS OF
COLOMBIA...WITH A SURGE IN ACTIVITY FROM MARACAIBO/APURE VENEZUELA
TO NORTHERN COLOMBIA ON DAY 02...WHEN IT IS TO FAVOR RAINFALL
AMOUNTS OF 20-35MM/DAY AND MAXIMA OF 50-75MM.

TROPICAL WAVES/EASTERLY WAVES 

INIT    F24     F36     F48     F60      F72      F84
32W     33W     36W     38W     40W      43W      46W
56W     57W     60W     62W     64W      65W      67W
64W     66W     68W     70W     72W      75W      77W
73W     75W     78W     80W     82W      85W      87W
83W     84W     86W     88W     89W      90W      92W 
105W    106W    108W    110W    113W     115W     116W    

THE WAVE ALONG 56W...AS IT ENTERS THE EASTERN CARIBBEAN...IT WILL
TEND TO SHEAR NORTH UNDER INFLUENCE OF DEEP MID/UPPER TROUGH
DOMINATING FLOW NORTH OF THE ISLANDS/EASTERN CARIBBEAN. AS A
RESULT...MOST ACTIVE CONVECTION IS EXPECTED NORTH OF 20N. ACROSS
THE LESSER ANTILLES WE ONLY FORESEE RAINFALL AMOUNTS OF
05-10MM/DAY AND MAXIMA OF 15MM...WHILE OVER PUERTO RICO AND THE
DOMINICAN REPUBLIC MAXIMA WILL PEAK AT 20-35MM.

THE PERTURBATION ALONG 64W IS INDUCED BY UPPER TROUGH OVER THE
EASTERN CARIBBEAN. IN INTERACTION WITH THE NEAR EQUATORIAL TROUGH
IT WILL FAVOR ORGANIZED CONVECTION FROM VENEZUELA-COLOMBIA TO
PANAMA...MOST INTENSE BETWEEN 48-84 HRS (SEE ABOVE FOR
DETAILS/RAINFALL AMOUNTS). 

THE WAVE ALONG 73W WILL ENHANCE CONVECTION ACROSS WESTERN
COLOMBIA/THE DARIEN IN PANAMA TO SUSTAIN RAINFALL AMOUNTS OF
10-15MM/DAY AND MAXIMA OF 30-60MM. SIMILAR AMOUNTS ARE EXPECTED
OVER COSTA RICA-NICARAGUA/NORTHEAST HONDURAS ON DAY 02...WHILE ON
DAY 03 MAXIMA OF 40-80MM IS EXPECTED FROM EL SALVADOR/HONDURAS TO
GUATEMALA/BELIZE.

THE WAVE ALONG 83W IS INTERACTING WITH TUTT OVER THE GULF OF
MEXICO IN SUPPORT OF ORGANIZED DEEP CONVECTION...TO AFFECT FROM
COSTA RICA TO EASTERN NICARAGUA/NORTHEAST HONDURAS EARLY IN THE
PERIOD WITH ACCUMULATION OF 15-25MM/DAY AND MAXIMA OF 35-70MM.
THIS EXPANDS ACROSS EL SALVADOR/HONDURAS TO GUATEMALA/BELIZE
THROUGH 48-60 HRS...WITH ACCUMULATION OF 20-35MM/DAY AND MAXIMA OF
50-75MM.

THE WAVE ALONG 105W IS TO INTERACT WITH THE EASTERN PACIFIC ITCZ
IN SUPPORT OF CONVECTION MAINLY TO THE SOUTH OF 15N. BUT SOME
ENHANCEMENT IS ALSO EXPECTED OVER MEXICO TO AFFECT
DURANGO/SOUTHERN CHIHUAHUA-SINALOA WITH MAXIMA OF 35-70MM THROUGH
36-42 HRS.

BROWN....NMC (JAMAICA)
GREENE...DM (BAHAMAS)
DAVISON...NCEP (USA)


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