TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 PM EDT TUE SEP 26 2023

FORECAST BULLETIN 26 SEP 2023 AT 1830 UTC: THE NATIONAL HURRICANE
CENTER IS MONITORING A COUPLE OF SYSTEMS IN THE ATLANTIC
BASIN...TROPICAL STORM PHILIPPE AND A BROAD AREA OF LOW PRESSURE
THAT HAS BEEN NAMED AL91. AL91...CURRENTLY ALONG 37W IS MOVING
INTO A FAVORABLE ENVIRONMENT FOR DEVELOPMENT...AND THE NATIONAL
HURRICANE CENTER IS SUGGESTING A 80 PERCENT CHANCE OF TROPICAL
CYCLONE FORMATION IN THE NEXT 48 HOURS...AND A 90 PERCENT CHANCE
OF FORMATION THROUGH 7 DAYS. THE NATIONAL HURRICANE CENTER EXPECTS
FURTHER DEVELOPMENT...AND A TROPICAL DEPRESSION COULD DEVELOP IN
THE NEXT DAY OR TWO AS IT MOVES TO THE WEST NORTHWEST. THE LATEST
GUIDANCE SUGGESTS THAT THIS SYSTEM WILL REMAIN TO THE EAST OF THE
LESSER ANTILLES...BUT WE WILL MONITOR THE LATEST FORECAST BY THE
NATIONAL HURRICANE CENTER. TROPICAL STORM PHILIPPE SEEMS TO BE
STRUGGLING WITH A WEST SOUTHWESTERLY SHEAR AS IT CONTINUES TO MOVE
WEST. BASED ON THE LATEST FORECAST BY THE NATIONAL HURRICANE
CENTER...PHILIPPE WILL REMAIN TO THE NORTHEAST OF THE LEEWARDS
THROUGH THE REST OF THE WORKWEEK AS IS SLOWLY MOVES WEST OR WEST
NORTHWEST. HOWEVER...THERE IS SOME UNCERTAINTY IN THE LATTER PART
OF THE 5-DAY FORECAST AS PHILIPPE WEAKENS SLOWLY.

AT THE SURFACE...THERE IS A HIGH PRESSURE ACROSS THE EAST CENTRAL
ATLANTIC...WHICH WILL PREVAIL THROUGH THIS WEEK. THEN THERE IS A
TROUGH OF LOW PRESSURE ACROSS THE SOUTHWESTERN GULF OF
MEXICO...NEAR THE YUCATAN PENINSULA...WHICH IS EXPECTED TO MEANDER
OVER THE SOUTHWEST GULF OF MEXICO FOR THE NEXT FEW DAYS. IN THE
MID LEVELS...A BROAD HIGH PRESSURE IS DOMINATING THE ATLANTIC WITH
ITS CENTER TO THE NORTH OF THE GREATER ANTILLES. THERE IS ALSO A
MID LEVEL TROUGH OVER THE YUCATAN PENINSULA...WHICH IS HELPING THE
INSTABILITY AND THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS
TODAY. UPPER LEVEL HIGH PRESSURES ACROSS THE TROPICAL ATLANTIC AND
THE CENTRAL CARIBBEAN IS HELPING KEEP A SOMEWHAT STABLE
ATMOSPHERE...THOUGH THE STRONG UPPER LEVEL WINDS ASSOCIATED WITH
THEM IS PROVIDING VENTILATION FOR THE DEVELOPMENT OF SUSTAINED
SHOWERS IN THE PERIPHERY OF THE HIGH PRESSURE CIRCULATION. THERE
IS AN UPPER LEVEL TROUGH ACROSS THE SOUTHWEST GULF OF MEXICO THAT
IS WEAKENING A LITTLE EACH DAY OVER THE NEXT FEW DAYS.

IN MEXICO...THE YUCATAN PENINSULA AND SOUTHERN MEXICO ARE EXPECTED
TO OBSERVE RAINFALL EACH DAY OVER THE 3-DAY FORECAST PERIOD...DUE
TO THE LOW PRESSURE IN THE AREA...THAT BRING MOISTURE...COMBINES
WITH THE MID AND UPPER LEVEL TROUGHS TO THE WEST OF THE PENINSULA.
THURSDAY INTO FRIDAY COULD BE THE WETTEST DAY ACROSS THE AREA AS A
TROPICAL WAVE MOVES INTO THAT AREA. THE WEST COAST OF OF MEXICO IS
ALSO EXPECTED TO OBSERVE SHOWERS AND THUNDERSTORMS AT TIMES OVER
THE NEXT SEVERAL DAYS...THOUGH GENERALLY IN THE ORDER OF
05-10MM/DAY WITH MAX UP TO 25MM. NORTHEAST MEXICO...NEAR COAHUILA
AND NUEVO LEON IS FORECAST TO OBSERVE RAINFALL ON WEDNESDAY...THEN
SOME RAINFALL IS FORECAST FROM NUEVO LEON INTO TAMAULIPAS. THE
RAINFALL TOTALS ARE FORECAST TO BE GENERALLY IN THE ORDER OF
05-10MM/DAY WITH MAX AMOUNTS UP TO 15-20MM.

IN THE CARIBBEAN...MOSTLY EASTERLY TRADE WINDS WILL PREVAIL OVER
THE AREA...BUT DEEP MOISTURE FROM THE SOUTH IS MOVING NORTH
THROUGH THE WESTERN CARIBBEAN. IN TERMS OF RAINFALL...MOST OF THE
RAINFALL ACROSS THE LESSER ANTILLES IS EXPECTED TO BE DUE TO BRIEF
SHOWERS. LOCALLY INDUCED SHOWERS AND THUNDERSTORMS COULD AFFECT
ISOLATED AREAS OF PR AND HISPANIOLA IN THE AFTERNOON HOURS EACH
DAY...OTHERWISE BRIEF TRADE WIND SHOWERS WOULD AFFECT THE WINDWARD
SIDE OF THE GREATER ANTILLES. RAINFALL TOTALS OF UP TO 10MM WOULD
BE GENERALLY EXPECTED ACROSS HISPANIOLA...PUERTO RICO AND USVI
TODAY...WHILE 15MM IS POSSIBLE ACROSS THE LESSER ANTILLES.
SLIGHTLY HIGHER AMOUNTS ARE EXPECTED ON WEDNESDAY... UP TO 15MM
ACROSS THE GREATER ANTILLES BUT ISOLATED AMOUNTS UP TO 25MM OR
EVEN HIGHER COULD BE OBSERVED. WESTERN CUBA HAS A CHANCE OF MORE
SIGNIFICANT RAINFALL TODAY AND THURSDAY...UP TO 35MM DUE TO THE
SIGNIFICANT MOISTURE THAT IS MOVING IN AND THE SOMEWHAT STRONG
WINDS ALOFT.

IN CENTRAL AMERICA...THE DEEP MOISTURE WILL HELP IN THE
DEVELOPMENT OF SHOWERS AND THUNDERSTORMS THROUGH THURSDAY. SOME
AREAS OF COSTA RICA AND PANAMA WILL OBSERVE UP TO 25MM
TODAY...WHILE EL SALVADOR AND GUATEMALA COULD OBSERVE UP TO 35MM.
RAIN INCREASES ON WEDNESDAY ACROSS COSTA RICA AND PANAMA...WITH
PORTIONS OBSERVING MAX VALUES UP TO AROUND 50MM WITH
THUNDERSTORMS...THEN EL SALVADOR AND GUATEMALA OBSERVING UP TO
20-35MM. EVEN DEEPER MOISTURE AND HIGHER MID LEVEL VORTICITY WILL
CAUSE THE WESTERN SECTIONS OF PANAMA INTO EASTERN COSTA RICA TO BE
AT RISK OF SIGNIFICANT RAIN ON THURSDAY INTO FRIDAY. THE MODEL
GUIDANCE IS SUGGESTING AS MUCH AS 100MM OF RAIN IS POSSIBLE ACROSS
ISOLATED AREAS. MOST OF HONDURAS AND NICARAGUA WILL OBSERVE MAX
TOTALS BETWEEN 15 AND 25MM. GUATEMALA...HOWEVER...COULD OBSERVE
SIGNIFICANT RAIN...UP TO 40-80MM ON THURSDAY INTO FRIDAY AS THE
TROPICAL WAVE REACHES THE AREA.

IN NORTHERN SOUTH AMERICA...WESTERN COLOMBIA INTO WESTERN ECUADOR
ARE THE AREAS WITH THE MOST SIGNIFICANT RAINFALL WITH TOTALS UP TO
AROUND 50 TO 70MM EXPECTED EACH DAY THROUGH FRIDAY. THE REST OF
COLOMBIA AND MOST OF VENEZUELA IS EXPECTED TO OBSERVE RAINFALL
EACH DAY BUT IN THE ORDER OF 05-10MM.DAY WITH MAX VALUES OF
15-25MM FOR THE MOST PART. NORTHERN PERU AND EASTERN ECUADOR IS
FORECAST TO OBSERVE SIMILAR AMOUNTS...GENERALLY 05-10MM AND UP TO
20MM EACH DAY. THE GUIANAS ARE FORECAST TO OBSERVE MINIMAL
RAINFALL EACH DAY...EXCEPT TODAY AS GUYANA IS FORECAST UP TO
20-35MM.

POSITIONS OF TROPICAL/EASTERLY WAVES INITIALIZED AT 12 UTC
TYPE SOF INIT 27/00 27/12 28/00 28/12 29/00 29/12 30/00 30/12
TW   19N  82W   85W   87W   88W   90W   92W   94W   96W   97W
TW   15N  37W   39W   42W   44W   46W   47W   48W   49W   50W

A TROPICAL WAVE IS INITIALIZED AT 82W AND TO THE SOUTH OF 19N. IT
HAS ABUNDANT MOISTURE ASSOCIATED WITH IT AND HAS MOVED INTO
CENTRAL AMERICA. THIS TROPICAL WAVE WILL HELP IN THE DEVELOPMENT
OF SHOWERS AND THUNDERSTORMS ACROSS CENTRAL AMERICA...DUE TO THE
DEEP TROPICAL MOISTURE ASSOCIATED WITH IT. THE TROPICAL WAVE IS
NOW FORECAST TO CONTINUE MOVING WEST BUT DECREASING ITS FORWARD
SPEED OVER THE NEXT FEW DAYS. THIS TROPICAL WAVE COULD BRING
SIGNIFICANT RAIN TO GUATEMALA AND SOUTHERN MEXICO ON THURSDAY INTO
FRIDAY.

A TROPICAL WAVE IS INITIALIZED AT 37W AND TO THE SOUTH OF
15N...ASSOCIATED WITH A BROAD LOW PRESSURE. THE NATIONAL HURRICANE
CENTER LABELED THIS AS AL91. THIS WAVE COULD DEVELOP INTO A
TROPICAL CYCLONE WITH GRADUAL DEVELOPMENT OVER THE NEXT DAY OR
TWO. THEREFORE...THE LATEST GUIDANCE HAS IT SLOWING DOWN
CONSIDERABLY AFTER WEDNESDAY...AND DEVELOPING IT INTO A TROPICAL
CYCLONE. THAT SAID...WE HAVE KEPT IT AS A TROPICAL WAVE UNTIL THE
NATIONAL HURRICANE CENTER OFFICIALLY LABELS IT AS A TROPICAL
CYCLONE. THE GLOBAL MODELS ARE SUGGESTING THIS SYSTEM COULD
DEVELOP INTO A TROPICAL CYCLONE BUT REMAIN IN THE ATLANTIC WATERS
EAST OF THE LEEWARDS. ONE SHOULD MONITOR THE LATEST BULLETINS BY
THE NATIONAL HURRICANE CENTER REGARDING THIS SYSTEM.

ALAMO...WPC (USA)