Prognostic Meteorological Discussion
Issued by NWS
Issued by NWS
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642 FXCA20 KWBC 181854 PMDCA TROPICAL DISCUSSION - INTERNATIONAL DESKS NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 254 PM EDT WED SEP 18 2024 FORECAST BULLETIN 18 SEP 2024 AT 18 UTC: NOTE...A TROPOSPHERIC KELVIN WAVE IS FORECAST TO ENTER CENTRAL AMERICA AND MEXICO THIS WEEKEND. AS THIS COMBINES WITH THE CYCLOGENETIC IMPACTS OF AN UPPER TROUGH DEEPENING ACROSS THE GULF OF MEXICO/NORTHERN CENTRAL AMERICA...EXPECT THE POTENTIAL FOR THE FORMATION OF A BAROCLINIC CENTRAL AMERICAN GYRE. ALTHOUGH THIS EVOLUTION IS EXPECTED PAST THE CURRENT FORECAST CYCLE...IT IS IMPORTANT TO CONSIDER MONITORING THIS SITUATION. IN THE MID-UPPER LEVELS...A QUASI-STATIONARY AND AMPLIFIED RIDGE/TROUGH PATTERN HAS ESTABLISHED. THIS CONSISTS OF A MASSIVE RIDGE CENTERING OVER CENTRAL MEXICO AND A TROUGH EXTENDING FROM THE EASTERN USA INTO THE YUCATAN PENINSULA REGION. INTENSE NORTHERLY FLOW IN THE EASTERN PERIPHERY OF THE RIDGE WILL LIKELY AMPLIFY THE UPPER TROUGH...TO DEVELOP AN AXIS INTO GUATEMALA/EL SALVADOR AND REGIONS OFFSHORE BY FRIDAY. IN THE LOWER LEVELS...HIGH VALUES OF AVAILABLE MOISTURE ARE PRESENT IN THE CENTRAL AND WESTERN CARIBBEAN. WAVES IN THE TRADES ARE PROPAGATING ACROSS THE REGION BUT THEY ARE ILL-DEFINED AT THIS TIME (SEE BELOW FOR POSITIONS AND IMPACTS). REGARDLESS OF WAVE STRUCTURE...THE SLOW DOWN OF PERTURBATIONS PROPAGATING IN THE TRADES IS EXPECTED TO FAVOR A GRADUAL INCREASE IN MOISTURE AND ASSOCIATED PRECIPITATING CONVECTION IN CENTRAL AMERICA. ALSO OF RELEVANCE...WESTERLIES ARE FORECAST TO GRADUALLY INTENSIFY ALONG THE SOUTHERN FRINGES OF THE ITCZ/MONSOON TROUGH IN THE EASTERN PACIFIC...WHICH WILL RESULT IN INTERMITTENT PERIODS OF HEAVY RAIN-PRODUCING CONVECTION IN WESTERN PANAMA AND THE PACIFIC BASIN OF COSTA RICA. THROUGH EARLY FRIDAY MOST ACTIVITY WILL ORGANIZE WITH AN EASTERLY WAVE (SEE BELOW FOR POSITIONS AND RAINFALL ACCUMULATION). HOWEVER...AS THE CAG STARTS TO ORGANIZE AND LONG FETCH WESTERLIES IMPACT SOUTHERN CENTRAL AMERICA STARTING ON FRIDAY...EXPECT HEAVY RAINFALL TO START DEVELOPING ON FRIDAY THROUGH EARLY SATURDAY IN COSTA RICA AND WEST PANAMA. ON FRIDAY INTO EARLY SATURDAY EXPECT MAXIMA OF 50-100MM/DAY IN SOUTHERN COSTA RICA AND WEST PANAMA...WHILE IN CENTRAL/EAST PANAMA AND WESTERN COLOMBIA EXPECT MAXIMA OF 25-50MM. ALSO IN ASSOCIATION WITH THE PERSISTENT UPPER TROUGH ACROSS THE SOUTHEAST USA...A MOIST PLUME IS FORECAST TO CONTINUE ACROSS THE NORTHWEST BAHAMAS AND WEST CUBA. THIS WILL CONTINUE TO FAVOR SCATTERED CONVECTION ON A DAILY BASIS AND MODERATE RAINFALL ACCUMULATION. THROUGH EARLY THURSDAY EXPECT MAXIMA GENERALLY IN THE 15-35MM/DAY RANGE. GIVEN ENHANCED VENTILATION AND INSTABILITY...EXPECT A SLIGHT RISK FOR SEVERITY IN THE NORTHWEST BAHAMAS ON THURSDAY AND FRIDAY...WHILE IN CUBA EXPECT A MARGINAL RISK DEVELOPING ON FRIDAY. QUIET CONDITIONS FOR THIS TIME OF THE YEAR ARE EXPECTED IN MOST OF THE EASTERN CARIBBEAN. ALTHOUGH A SURFACE TROUGH IS PRESENT ACROSS THE WINDWARD ISLANDS ON WEDNESDAY AND IS FORECAST ON THURSDAY...LIMITED AMOUNTS OF AVAILABLE MOISTURE WILL RESULT IN VERY CONSERVATIVE ACCUMULATION FOR MID-SEPTEMBER. EASTERLY/TROPICAL WAVES INITIALIZED AT 12 UTC TYPE INIT SOF 19/00 19/12 20/00 20/12 21/00 21/12 22/00 22/12 EW 77W 16N 79W 82W 84W 85W 87W CAG ----- ----- TW 89W 17N 92W 94W 97W DISS ----- ----- ----- ----- AN EASTERLY WAVE IS PROPAGATING ACROSS PANAMA ON WEDNESDAY TO FAVOR MAXIMA OF 20-35MM. ON THURSDAY...IT WILL FAVOR MAXIMA OF 35-70MM IN WEST PANAMA AND SOUTHERN COSTA RICA...AND MAXIMA OF 30-60MM IN EAST NICARAGUA AND EASTERN HONDURAS. IN WEST NICARAGUA/GULF OF FONSECA REGION IT WILL FAVOR MAXIMA OF 20-45MM. ON FRIDAY...THE WAVE WILL FAVOR MAXIMA OF 40-80MM IN NORTHERN NICARAGUA...HONDURAS AND EL SALVADOR...WHILE IN SOUTHERN NICARAGUA AND NORTHERN COSTA RICA IT WILL FAVOR MAXIMA OF 25-50MM. AN ILL-DEFINED TROPICAL WAVE IS PROPAGATING ACROSS GUATEMALA/SOUTHEAST MEXICO ON WEDNESDAY TO FAVOR GENERALLY MAXIMA OF 20-35MM. ON THURSDAY...THIS WILL FAVOR MAXIMA OF 15-25MM FROM OAXACA/SOUTHERN VERACRUZ INTO GUERRERO/MORELOS WHILE DISSIPATING. LEDESMA...(WPC) TINOCO...(WPC) GALVEZ...(WPC) $$