TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 PM EDT TUE JUL 23 2024

FORECAST BULLETIN 23 JUL 2024 AT 1815 UTC: A RELATIVELY DENSE
SAHARAN DUST LAYER (SAL) IS AFFECTING PORTIONS OF THE WESTERN
CARIBBEAN...THE NORTHERN BAHAMAS...AND PORTIONS OF CENTRAL AMERICA
INTO THE YUCATAN PENINSULA TODAY. THE SAL OVER THE CARIBBEAN
REGION IS EXPECTED TO CONTINUE MOVING NORTH NORTHWEST OVER THE
NEXT FEW DAYS. THIS WILL CAUSE THE SAL TO AFFECT EASTERN MEXICO
AND THE GULF OF MEXICO BY MIDWEEK...BUT CLEANER AIR WILL MOVE INTO
THE CARIBBEAN REGION OVER THE NEXT FEW DAYS. ANOTHER RELATIVELY
DENSE SAL IS MOVING THROUGH THE TROPICAL ATLANTIC AND WILL START
REACHING THE LESSER ANTILLES ON WEDNESDAY. ACCORDING TO THE LATEST
GUIDANCE...THE CONCENTRATION OF THIS NEXT SAL EVENT COULD BE
SIMILAR TO THE ONE RECENTLY OBSERVED OVER THE CARIBBEAN. IN TERMS
OF AVAILABLE MOISTURE...NORMAL TO BELOW NORMAL MOISTURE IS BEING
OBSERVED ACROSS THE CARIBBEAN...WITH THE DRIEST PATCH OF MOISTURE
EXPECTED OVER CENTRAL AMERICA TODAY...ESPECIALLY OVER NICARAGUA
AND HONDURAS. WHILE THE DRIEST PATCH OF MOISTURE MOVES FROM
NORTHWEST INTO THE YUCATAN PENINSULA BY LATE TONIGHT INTO
WEDNESDAY...A GRADUAL INCREASE IN MOISTURE WILL BE OBSERVED OVER
THE CARIBBEAN...WITH MOISTURE MOVING IN FROM THE SOUTH. THIS WILL
CAUSE THE GREATER ANTILLES TO AND CENTRAL AMERICA TO HAVE ABOVE
NORMAL MOISTURE LATE WEDNESDAY INTO THURSDAY.

ACCORDING TO THE NATIONAL HURRICANE CENTER...THERE IS NO CYCLONE
ACTIVITY EXPECTED OVER THE NEXT 7 DAYS ACROSS THE ATLANTIC BASIN.
HOWEVER...THERE ARE A COUPLE OF DISTURBANCES IN THE EAST PACIFIC
THAT THE NATIONAL HURRICANE CENTER IS MONITORING FOR POSSIBLE
TROPICAL CYCLONE FORMATION. ONE IS AN AREA OF LOW PRESSURE WITH A
TROPICAL WAVE AT AROUND 108W AND ANOTHER NEAR 117W...BOTH OF WHICH
HAVE A LOW CHANCE OF TROPICAL CYCLONE FORMATION IN 7 DAYS WITH A
PROBABILITY OF 30 PERCENT AND 20 PERCENT RESPECTIVELY. REGARDLESS
OF DEVELOPMENT...BOTH OF THESE DISTURBANCES ARE FORECAST TO
CONTINUE MOVING WEST AND INTO OPEN WATERS. 

AT THE SURFACE...A STRONG HIGH PRESSURE CONTINUES TO DOMINATE THE
ATLANTIC...CAUSING EASTERLY TO SOUTHEASTERLY WINDS ACROSS THE
ATLANTIC...CARIBBEAN AND THEN SOUTHERLY WINDS ACROSS THE WESTERN
GULF OF MEXICO. THERE IS ALSO A SFC LOW OVER NORTHERN
MEXICO...WHICH IS CONTRIBUTING TO THE SOUTHERLY WINDS OVER THE
WESTERN GULF OF MEXICO AS WELL AS EASTERN MEXICO. A SFC LOW OVER
NORTHWESTERN COLOMBIA WILL MOVE INTO THE CARIBBEAN TODAY. THIS IS
CAUSING A TIGHTENING OF THE PRESSURE GRADIENT ACROSS THE CARIBBEAN
SEA AND THEREFORE LOCALLY STRONGER WINDS OVER THE CARIBBEAN
WATERS. THIS SFC LOW WILL MEANDER OVER THE SOUTHERN CARIBBEAN FOR
THE NEXT FEW DAYS...NOT ONLY CAUSING PERSISTENT LOCALLY STRONGER
WINDS OVER THE CARIBBEAN...BUT ALSO CAUSING MOISTURE CONVERGENCE
OVER COSTA RICA AND PANAMA.

THE UPPER LEVELS ARE PROVIDING SOME SUPPORT FOR CONVECTION ACROSS
THE WESTERN GULF OF MEXICO AND INTO PORTIONS OF MEXICO. THIS IS
DUE TO AN UPPER LOW OVER NORTHEASTERN MEXICO COMBINING WITH DEEP
MOISTURE OVER THE AREA. THIS UPPER LOW WILL WEAKEN BY
TUESDAY...BUT IT WILL BE ABSORBED BY A LARGER UPPER TROUGH
DOMINATING MOST OF THE CENTRAL U.S. INTO NORTHEASTERN MEXICO.
THERE IS ANOTHER UPPER LOW...THIS ONE ACROSS THE WESTERN TROPICAL
ATLANTIC JUST EAST OF THE BAHAMAS...BUT THE AIR IS VERY DRY OVER
THAT AREA...AND THEREFORE THE CONVECTION IS LIMITED.

THE LOW TO MID LEVEL RELATIVE HUMIDITY ACROSS THE TROPICAL REGION
SHOWS THAT THE MOISTURE ALONG THE ITCZ INTO MEXICO AND THE GULF OF
MEXICO WILL PERSIST FOR THE NEXT FEW DAYS...WITH THE EXCEPTION OF
THE DRIER AIR WITH SAHARAN DUST MOVING INTO THE YUCATAN PENINSULA
TODAY INTO WEDNESDAY. THIS DEEPER MOISTURE WILL COMBINE WITH THE
AFOREMENTIONED UPPER TROUGH ACROSS MEXICO TO CAUSE PERSISTENT
SHOWER ACTIVITY OVER MANY SECTORS OF CENTRAL...EASTERN...AND
SOUTHERN MEXICO TODAY...THEN THE HEAVIEST RAINFALL ON WEDNESDAY
AND THURSDAY WILL BE MORE CONCENTRATED ACROSS THE CENTRAL PORTIONS
OF MEXICO. EVEN THOUGH THE SIERRA MADRE OCCIDENTAL IN MEXICO IS ON
THE CONVERGENT SIDE OF THE UPPER TROUGH...THE LOW LEVEL WIND FLOW
WILL BE FROM THE EASTERN PACIFIC INTO THE SIERRA MADRE
OCCIDENTAL...WHICH WILL PROVIDE MOISTURE TO MOVE INLAND AND SHOWER
ACTIVITY IS EXPECTED TO DEVELOP DUE TO OROGRAPHIC
LIFTING...ESPECIALLY TODAY. THEREFORE...THE COMBINATION OF FACTORS
WILL CAUSE MANY SECTORS IN MEXICO TO OBSERVE RAINFALL OVER THE
NEXT FEW DAYS...BUT THE CENTRAL PORTIONS ARE FORECAST TO HAVE THE
MORE SIGNIFICANT RAIN FROM WEDNESDAY THROUGH EARLY FRIDAY.

ACROSS CENTRAL AMERICA...THE LOCATIONS WITH MOST PRECIPITATION ARE
EXPECTED TO BE AREAS IN AND AROUND COSTA RICA AND PANAMA...DUE TO
THE AFOREMENTIONED SFC LOW PRESSURE AND PERSISTENT DEEP MOISTURE
OVER THE AREA. HOWEVER...THE CARIBBEAN COAST OF HONDURAS AND
NICARAGUA WILL ALSO HAVE SIGNIFICANT AMOUNTS OF RAIN...ESPECIALLY
ON WEDNESDAY AND THURSDAY AS THE SFC LOW MOVES CLOSER TO
NICARAGUA...CAUSING DAILY RAIN TOTALS OF AROUND 30-45MM ON
WEDNESDAY AND THURSDAY ACCORDING TO THE GFS MODEL. NORTHWESTERN
COLOMBIA WILL HAVE LOCALIZED AMOUNTS OF RAIN NEAR 60MM TODAY...AND
UP TO 75MM ON WEDNESDAY...BUT THURSDAY INTO FRIDAY...THE MODEL
GUIDANCE SHOWS MUCH LESS RAIN OVER NORTHWESTERN COLOMBIA.
HOWEVER...WE DECIDED TO HAVE MORE RAIN IN THE FORECAST THAN THE
MODELS AS A TROPICAL WAVE WILL BE PASSING THROUGH THE AREA. THE
GFS MODEL CONTINUES TO SHOW A BETTER HANDLE ON THE LOCALIZED
CONVECTION ACCORDING TO THE RECENT SATELLITE IMAGERY AND MODEL
INITIALIZATION. FOR THAT REASON...WE ARE SHOWING MAX RAINFALL
TOTALS IN OUR FORECAST MORE ALIGNED WITH THE GFS...BUT KEEP IN
MIND THAT THESE MAX VALUES ARE ISOLATED.

ACROSS NORTHERN SOUTH AMERICA...ANOTHER SECTOR TO OBSERVE IS THE
CENTRAL TO EASTERN SECTIONS OF VENEZUELA...WHICH IS EXPECTED TO
HAVE LOCALIZED HIGHER AMOUNTS OF RAIN THAN JUST ABOUT ANYWHERE
ELSE OVER NORTHERN SOUTH AMERICA. THE MID TO UPPER LEVELS ARE NOT
CAUSING CONDUCIVE FOR ENHANCED CONVECTIVE SUPPORT...BUT THE LOW
LEVEL WINDS AND DEEP MOISTURE WILL COMBINE WITH THE OROGRAPHIC
LIFTING OVER THE AREA TO CAUSE DAILY SHOWERS AND THUNDERSTORMS.
ACROSS THE CARIBBEAN ISLANDS AND INTO THE BAHAMAS...MODEST AMOUNTS
OF RAIN ARE EXPECTED OVER THE NEXT FEW DAYS GIVEN THE RELATIVELY
DRY AIR. THE GLOBAL MODEL GUIDANCE IS SUGGESTING MAX VALUES OF
ABOUT 50 TO 60MM OVER ISOLATED AREAS FOR A 3-DAY TOTAL
PRECIPITATION TOTAL. HOWEVER...MOST AREAS COULD OBSERVE A 3-DAY
MAX AMOUNT OF AROUND 35-40MM. THIS COULD MEAN DAILY MAX VALUES OF
UNDER 25MM ACROSS THE ISLANDS THROUGH EARLY FRIDAY. THAT BEING
SAID...THERE IS A MARGINAL TO SLIGHT RISK FOR STRONG THUNDERSTORMS
AND SQUALLY WEATHER ACROSS PORTIONS OF SOUTHERN CUBA..SOUTHERN
BAHAMAS...THE TURKS AND CAICOS...AND HAITI ON THURSDAY INTO FRIDAY
MORNING. THIS IS DUE TO COLD MID-LEVEL TEMPS...COLDER THAN -8C AND
BEING IN THE DIVERGENT SIDE OF THE UPPER TROUGH.



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