TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
230 PM EDT THU JUL 18 2024

FORECAST BULLETIN 18 JUL 2024 AT 1830 UTC: A SURFACE HIGH PRESSURE
ACROSS THE CENTRAL ATLANTIC CONTINUES TO DOMINATE THE ATLANTIC
BASIN...AND IT WILL CONTINUE OVER THE AREA AT LEAST THROUGH THE
REST OF THE WEEK. THERE IS A WEAK SFC LOW ACROSS THE SOUTHWESTERN
CARIBBEAN...JUST NORTH OF PANAMA...WHICH WILL CAUSE MOISTURE FROM
THE MONSOON TROUGH TO MOVE INTO THE WEST COAST OF COLOMBIA
TODAY...AS WELL AS PANAMA. HOWEVER WITH EACH PASSING DAY THE LOW
WILL SLOWLY MOVE WEST AND THE MOISTURE ADVECTION WILL FAVOR OTHER
PORTIONS OF PANAMA...COSTA RICA AND NICARAGUA AFTER TODAY. MOST OF
THE TROPICAL ATLANTIC CONTINUES TO BE FAIRLY QUIET AS A LARGE
PLUME OF SAHARAN DUST IS PRESENT OVER THE AREA...WITH THE
EXCEPTION OF AREAS ALONG THE ITCZ / MONSOON TROUGH. THERE ARE ALSO
A FEW TROPICAL WAVES IN THE ATLANTIC BASIN...CURRENTLY NEAR 53W
AND ANOTHER ONE NEAR 74W. THESE TROPICAL WAVES ARE CAUSING LOCALLY
HIGHER AREAS OF MOISTURE...WHICH WILL HELP INCREASE THE CHANCES OF
SHOWERS AS THEY APPROACH LAND AREAS. IN THE MID LEVELS...THERE IS
A LARGE HIGH PRESSURE ACROSS THE CENTRAL ATLANTIC...EXPANDING INTO
THE GULF OF MEXICO...THOUGH A MID LEVEL TROUGH IS PRESENT JUST
EAST OF THE LESSER ANTILLES...ALIGNED WITH THE LOCATION OF THE
TROPICAL WAVE. THERE ARE ALSO WEAK MID LEVEL LOWS ACROSS THE
MONSOON TROUGH IN THE EAST PACIFIC. THERE IS AN UPPER LOW ACROSS
THE WESTERN TROPICAL ATLANTIC...CENTERED AROUND 29N/79W WITH A
TROUGH AXIS EXTENDING SOUTH INTO THE CENTRAL CARIBBEAN.

IN TERMS OF RAINFALL ACCUMULATIONS...THE OVERALL PATTERN HAS NOT
CHANGED MUCH FROM WHAT WAS OBSERVED YESTERDAY. THE LOCAL MAXIMUM
RAINFALL OVER NORTHERN SOUTH AMERICA COULD BE ATTRIBUTED TO THE
INTERACTION BETWEEN THE DEEP AVAILABLE MOISTURE WITH THE LOCAL
TERRAIN EFFECTS. THE MID AND UPPER LEVEL DYNAMICS ARE NOT
PARTICULARLY FAVORABLE FOR PROLONGED RISING MOTION OR VENTILATION
ACROSS THE AREA. THAT SAID...THE AFOREMENTIONED LOW PRESSURE NEAR
PANAMA WILL BRING PERSISTENT MOISTURE FROM THE MONSOON TROUGH INTO
WESTERN COLOMBIA TODAY...BUT AS THE LOW SLOWLY MOVES WEST...THE
ONSHORE FLOW INTO WESTERN COLOMBIA WILL DECREASE WITH EACH PASSING
DAY. THE SECTION ACROSS NORTHERN SOUTH AMERICA WITH THE MOST
SIGNIFICANT RAINFALL IS EXPECTED TO BE ACROSS CENTRAL TO EASTERN
VENEZUELA INTO WESTERN GUYANA. THE LATEST MODEL GUIDANCE IS
SUGGESTING DAILY MAX TOTALS OF 30-60MM OVER EASTERN
VENEZUELA...WHILE THE WESTERN SECTION OF GUYANA IS FORECAST DAILY
MAX TOTALS NEAR 35-45MM. WESTERN COLOMBIA COULD HAVE AS MUCH AS
50MM TODAY...BUT FRIDAY INTO THE WEEKEND COULD HAVE DAILY MAX
RAINFALL TOTALS CLOSER TO 30MM.

CENTRAL AMERICA COULD HAVE SOME AREAS WITH AN ENHANCED
PRECIPITATION THIS WEEKEND. THIS WILL BE DUE TO THE SFC LOW
PRESSURE MOVING WEST AND BRINGING MOISTURE TO OTHER PORTIONS OF
CENTRAL AMERICA INTO NICARAGUA. THERE IS ALSO A TROPICAL WAVE
MOVING WEST...EXPECTED TO HAVE AXIS OVER HONDURAS AND NICARAGUA BY
FRIDAY NIGHT INTO SATURDAY. THEREFORE...THE CHANCES OF RAIN WILL
INCREASE WITH THE INCREASE IN MOISTURE AND THE PASSING OF THE
TROPICAL WAVE. AT THIS TIME...THE DIFFERENT GLOBAL MODELS INDICATE
THAT OVER THE NEXT 3 DAYS...THE RAINFALL TOTAL COULD ACCUMULATE AS
MUCH AS 75 TO 100MM OVER MANY SECTORS OF COSTA RICA AND
NICARAGUA...THOUGH THE GFS MODEL IS VERY BULLISH IN THE RAINFALL
AMOUNTS OVER PORTIONS OF WESTERN PANAMA AND EL
SALVADOR...SUGGESTING AS MUCH AS 100MM OVER ISOLATED AREAS. GIVEN
THE LATEST SATELLITE IMAGERY AND MODEL INITIALIZATION...THE GFS
SOLUTION DOES NOT SEEM TO BE EXAGGERATED AS THERE IS CURRENTLY
SIGNIFICANT CONVECTION OVER THE AREA AND RECENT RAINFALL
OBSERVATIONS WOULD AGREE THAT THE GFS HAS A BETTER HANDLE ON THE
AMOUNTS OF RAIN.

ACROSS MEXICO...THE WIDESPREAD COVERAGE OF RAIN IS EXPECTED TO
CONTINUE INTO THE WEEKEND. IN FACT...BOTH THE GFS AND ECMWF MODELS
INDICATE THAT OVER THE NEXT 72 HOURS...ONLY A SMALL PORTION OF THE
COUNTRY WOULD RECEIVE NO RAIN. BASED ON THE 00Z GUIDANCE...THE
BAJA PENINSULA...EXTREME NORTHWESTERN SONORA...AND PORTIONS OF THE
TEXAS/MEXICO BORDER WOULD HAVE LITTLE TO NO RAIN OVER THE 3-DAY
PERIOD. BUT ESSENTIALLY THE REST OF THE COUNTRY IS FORECAST TO
RECEIVE SOME RAIN...ANS A GOOD PORTION OF IT MAY RECEIVE
SIGNIFICANT RAIN. IN PARTICULAR PORTIONS OF SINALOA AND
DURANGO...TO THE SOUTHEAST ALL THE WAY TO OAXACA AND VERACRUZ
COULD RECEIVE A 3-DAY TOTAL OF AROUND 30-60MM ACCORDING TO THE
GLOBAL MODELS. THIS IS DUE TO AN AREA OF MOISTURE CONVERGENCE
ALONG THE SIERRA MADRE AND ADJACENT AREAS THAT WILL HELP PROMOTE
PERSISTENT LIGHT TO MODERATE SHOWERS OVER THE AREA. A SFC HIGH
PRESSURE ACROSS THE EAST PACIFIC JUST WEST OF SOUTHWESTERN
MEXICO...A TROUGH OVER THE BAJA PENINSULA...AND EASTERLY WINDS
FROM THE GULF OF MEXICO...COMBINED WITH DIURNAL HEATING...WILL
CAUSE ONSHORE FLOW TO CONVERGE ALONG THE SIERRA MADRE OCCIDENTAL
AS WELL AS OTHER PORTIONS OF SOUTH CENTRAL MEXICO. THIS
CONVERGENCE WILL CAUSE DAILY RAIN VALUES BETWEEN 05-15MM WITH
LOCALIZED MAXIMA BETWEEN 20-50MM CAN BE EXPECTED ACROSS MANY
SECTORS OF MEXICO EACH DAY.

THE FORECAST RAINFALL AMOUNTS ACROSS THE CARIBBEAN ISLANDS IS
RELATIVELY MODEST TODAY AND SATURDAY INTO SUNDAY...BUT THE BIG
QUESTION IS HOW WILL THE TROPICAL WAVE AND DEEP MOISTURE WILL
INTERACT WITH THE EASTERN CARIBBEAN ISLANDS ON FRIDAY INTO
SATURDAY. THE GFS MODEL IS AN OUTLIER AND IS SUGGESTING AS MUCH AS
75MM OF RAIN ACROSS EASTERN PR ON FRIDAY INTO SATURDAY...WHILE THE
MODEL BLENDS AND ECMWF MODEL SUGGESTS CLOSER TO 30MM. GIVEN THE
AMOUNT OF SAHARAN DUST OVER THE CARIBBEAN AND THE LACK OF MID TO
UPPER LEVEL DYNAMICS...THE MODEL BLEND AND ECMWF SOLUTION SEEMS
MORE REALISTIC THAN THE BULLISH GFS SOLUTION. THOUGH SOMETIMES
SAHARAN DUST INCREASES UNCERTAINTY CONSIDERABLY. HOWEVER...AT THIS
TIME WE ARE FAVORING THE MODEL CONSENSUS AND SUGGESTING MODEST
RAIN TODAY AND ON SUNDAY...WITH UP TO 20-35MM OF RAIN ON FRIDAY
INTO SATURDAY ACROSS THE LESSER ANTILLES AND NORTHEAST CARIBBEAN.


ALAMO...(WPC)
FERNANDER...(BDM)
CLARKE...(CINWS)