Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
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108 FXCA20 KWBC 191732 PMDCA TROPICAL DISCUSSION - INTERNATIONAL DESKS NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 131 PM EDT THU SEP 19 2024 FORECAST BULLETIN 19 SEP 2024 AT 17 UTC: THE MAIN SYSTEM OF INTEREST IN THE FORECAST CYCLE IS THE EXPECTED DEVELOPMENT OF A BAROCLINIC CENTRAL AMERICAN GYRE OVER CENTRAL AMERICA BETWEEN FRIDAY AND SATURDAY. NOTE THAT THIS SYSTEM COULD BECOME A SIGNIFICANT EVENT GIVEN THAT IT IS FORECAST TO LAST NEARLY A WEEK AS IT MEANDERS NORTHWESTWARD TOWARDS SOUTHEAST MEXICO THROUGH LATE NEXT WEEK. CONSIDERING THAT CONFIDENCE ON FLOW EVOLUTION AND ESPECIALLY PRECIPITATION WITH CAG EVENTS DECAYS RAPIDLY WITH TIME...THE DISTRIBUTION OF THE AREAS AT HIGHEST RISK FOR EXCESSIVE RAINFALL IS STILL LOW PAST SUNDAY. ON THURSDAY...A QUASI-STATIONARY AMPLIFIED MID-UPPER FLOW PATTERN CONTINUES ESTABLISHED OVER AREAS NORTH OF 15N. OF SPECIAL INTEREST IS A POTENT UPPER RIDGE LOCATED OVER CENTRAL MEXICO...WHICH IS FAVORING THE AMPLIFICATION OF A ROBUST UPPER TROUGH TO ITS EAST. THIS TROUGH IS ALREADY EXTENDING ITS BASE INTO GUATEMALA AND EL SALVADOR. SUCH UNSEASONABLY STRONG UPPER TROUGH IS EXPECTED TO CONTINUE INTERACTING WITH THE MOIST POOL BUILDING ACROSS THE NORTHWEST CARIBBEAN...TO TRIGGER THE FORMATION OF THE CAG. CONFIDENCE IN THIS EVOLUTION IS INCREASING GIVEN THE EXPECTED ARRIVAL OF A KELVIN WAVE THIS WEEKEND. IN THE MEAN TIME...AN EASTERLY WAVE IS ENHANCING CONVECTION IN CENTRAL AMERICA IN COMBINATION WITH LONG FETCH LOW-LEVEL WESTERLIES PRESENT IN THE PACIFIC BASINS OF COSTA RICA AND PANAMA (SEE BELOW FOR WAVE POSITIONS AND RAINFALL AMOUNTS). BUT AS THE CAG FORMS...EXPECT THE WAVE TO DISSIPATE ON SATURDAY WHILE POTENTIAL RAINFALL ACCUMULATIONS CONTINUE TO INCREASE. BY FRIDAY...EXPECT THE HEAVIEST PRECIPITATION IN WEST PANAMA AND WEST COSTA RICA ...WHERE ENHANCED ONSHORE FLOW WILL FAVOR MAXIMA OF 40-80MM. AS THE CAG STARTS GAINING STRUCTURE...EXPECT SCATTERED HEAVY THUNDERSTORMS TO DOT MOST OF NORTHERN CENTRAL AMERICA WHERE EXPECT AMOUNTS IN THE 15-20MM/DAY AND MAXIMA OF 30-60MM RANGE. IN CENTRAL PANAMA EXPECT MAXIMA OF 20-45MM. ON SATURDAY...EXPECT AMOUNTS OF 20-40MM/DAY AND MAXIMA OF 50-100MM DEVELOPING IN MOST OF COSTA RICA AND SOUTHWEST NICARAGUA...AS SOUTHWESTERLY LOW-LEVEL WINDS START DEVELOPING WEST OF CENTRAL AMERICA. IN EL SALVADOR/HONDURAS/SOUTHERN GUATEMALA EXPECT MAXIMA OF 30-60MM. IN NORTHEAST NICARAGUA AND EAST HONDURAS EXPECT MAXIMA OF 20-45MM...WHILE ISOLATED SIMILAR AMOUNTS ARE EXPECTED IN SOUTHERN PANAMA. A SECONDARY REGION OF INTEREST ENCOMPASSES THE NORTHWEST BAHAMAS AND WEST CUBA...GIVEN DIRECT INFLUENCES OF THE AFOREMENTIONED UPPER TROUGH. GIVEN THAT THE TROUGH IS FORECAST TO PERSIST THROUGH SEVERAL DAYS IN THE REGION...IT WILL PROVIDE RECURRENT PERIODS OF VENTILATION TO SUSTAIN INTERMITTENT SCATTERED SHOWERS AND THUNDERSTORMS THROUGH THE ENTIRE FORECAST CYCLE. ON THURSDAY EXPECT MAXIMA OF 20-35MM AND A MARGINAL RISK FOR SEVERITY IN THE NORTHWEST BAHAMAS...WHILE IN WEST AND CENTRAL CUBA EXPECT MAXIMA OF 15-25MM. ON FRIDAY...EXPECT MAXIMA GENERALLY IN THE 15-25MM/DAY RANGE ACROSS BOTH THE NORTHWEST BAHAMAS AND WEST AND CENTRAL CUBA. EXPECT SIMILAR AMOUNTS ON SATURDAY...BUT A DECREASE IN THE SEVERITY RISK FOR CUBA. EASTERLY/TROPICAL WAVES INITIALIZED AT 12 UTC TYPE INIT SOF 20/00 20/12 21/00 21/12 22/00 22/12 23/00 23/12 EW 82W 18N 83W 85W 87W 89W CAG ----- ----- ----- TW 93W 22N 95W 98W 102W 105W 108W 111W 114W EXITS AN EASTERLY WAVE IS INITIALIZE AT 82W AND IS SLOWING DOWN AS IT ENTERS CENTRAL AMERICA ON THURSDAY...TO FAVOR MAXIMA OF 20-45MM IN EAST HONDURAS/EAST NICARAGUA AND NORTHERN COSTA RICA. IN SOUTHERN COSTA RICA AND WEST PANAMA EXPECT MAXIMA OF 35-70MM. SIMILAR AMOUNTS ARE EXPECTED IN THE GULF OF FONSECA REGION WITH A RISK FOR MCS FORMATION. ON FRIDAY...THE WAVE WILL ENHANCE CONVECTION IN HONDURAS AND EL SALVADOR PRIMARILY...TO FAVOR MAXIMA OF 30-60MM AND A GENERALIZED RISK FOR HEAVY THUNDERSTORMS. NOTE THAT IT IS FORECAST TO THEN BECOME ILL-DEFINED AS THE CAG ESTABLISHES OVER CENTRAL AMERICA. A TROPICAL WAVE IS INITIALIZED AT 92W AND TO THE SOUTH OF 22N. THIS WAVE IS ILL-DEFINED BUT WILL PROPAGATE ACROSS SOUTHERN MEXICO...STIMULATING CONVECTION LOCALLY OVER FROM JALISCO TO OAXACA TO FAVOR MAXIMA OF 20-35MM ON THURSDAY...FOLLOWED BY A DECREASE IN MAXIMA TO 15-20MM ON FRIDAY...AS IT PROPAGATES ACROSS SOUTHWEST MEXICO. THE WAVE IS FORECAST TO RAPIDLY EXIT THE COASTS OF JALISCO ON SATURDAY WITH LIMITED IMPACTS IN CONTINENTAL CONVECTION. JACKMAN...(BMS-BARBADOS) LEDESMA...(WPC) TINOCO...(WPC) GALVEZ...(WPC) $$