TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
915 AM EDT THU JUL 11 2024

WEEKLY DISCUSSION FOR PUERTO RICO AND THE USVI JUl 11/12UTC:
LATEST SATELLITE IMAGERY AND MODEL GUIDANCE SUGGESTS THAT SOME
SAHARAN DUST WILL BE MOVING INTO PR/USVI OVERNIGHT TONIGHT INTO
FRIDAY. THERE MAY BE A BRIEF REDUCTION IN SAHARAN DUST ON FRIDAY
NIGHT...BUT A MORE SIGNIFICANT CONCENTRATION OF SAHARAN DUST WILL
BE MOVING IN LATE FRIDAY NIGHT INTO VERY EARLY MONDAY. IN TERMS OF
PRECIPITABLE WATER...A DRYING TREND WILL START THROUGH THE DAY
TODAY...BOTTOMING OUT LATE TONIGHT...WITH VALUES FROM NEAR 2.0
INCHES THIS MORNING TO 1.6 INCHES TONIGHT. HOWEVER...THE
PRECIPITABLE WATER VALUES ARE FORECAST TO INCREASE QUICKLY
TOMORROW TO ABOVE NORMAL VALUES...REMAINING ABOVE NORMAL FROM
FRIDAY NIGHT THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK...WITH
PARTICULAR INTEREST ON FRIDAY AND SATURDAY NIGHT...WHERE
PRECIPITABLE WATER COULD BE AS MUCH AS 2 STANDARD DEVIATIONS ABOVE
NORMAL.

THIS SIGNIFICANT INCREASE IN MOISTURE IS DUE TO A TROPICAL WAVE
APPROACHING THE LOCAL ISLANDS. EVEN THOUGH THERE WILL BE A GOOD
CONCENTRATION OF SAHARAN DUST...THE INCREASE IN MOISTURE WILL AID
IN THE DEVELOPMENT OF SHOWERS AND THUNDERSTORMS ACROSS
PR/USVI...WITH EASTERN PR AND THE USVI HAVING GENERALLY SCATTERED
SHOWERS...WHILE WESTERN PR WOULD HAVE AFTERNOON THUNDERSTORMS WITH
THE LOCATION GREATLY INFLUENCED BY THE GENERAL WIND FLOW AND SEA
BREEZE CONVERGENCE. IT IS ALSO WORTH MENTIONING THAT THE UPPER
LEVEL DYNAMICS AND FALLING MID LEVEL TEMPERATURES COULD CAUSE
STRONG THUNDERSTORMS THIS WEEKEND INTO MONDAY ACROSS PUERTO RICO.
THE 500MB TEMPS WILL INCREASE TO AROUND -4C TONIGHT...WHICH IS
WELL ABOVE NORMAL...BUT WILL GRADUALLY START DECREASING ON
SATURDAY AND POSSIBLY BEING AS LOW AS -7 TO -8C BY SATURDAY NIGHT
THROUGH AT LEAST MONDAY. IN ADDITION...THERE IS SOME RIDGING IN
THE UPPER LEVELS THAT WILL SETTLE LATER TODAY INTO FRIDAY...BUT A
STRONG TUTT WILL RETROGRADE ACROSS THE TROPICAL
ATLANTIC...CENTERING NEAR 25N/63W BY SUNDAY MORNING...THEN NEAR
24.5N/65.5W BY SUNDAY AFTERNOON. A RETROGRADING TUTT SUCH AS THIS
ONE WOULD NORMALLY ENHANCE CONVECTION AHEAD OF IT...AND THUS COULD
INCREASE INSTABILITY OVER OR/USVI ON SUNDAY.

BASED ON THIS SYNOPTIC PATTERN SETUP...STRONG THUNDERSTORMS COULD
OCCUR ON SATURDAY AND SUNDAY. IF WE CONSIDER THE OUTPUT FROM THE
EGDI AND GR02T ALGORITHMS...THERE IS A CHANCE OF SCATTERED
THUNDERSTORMS FROM SATURDAY INTO MONDAY...WITH A SLIGHT TO
MODERATE CHANCE OF STRONG THUNDERSTORMS ON SATURDAY AND SUNDAY.
THE GR02T ALGORITHM DOES INDICATE A BRIEF WINDOW OF TIME ON SUNDAY
AFTERNOON WITH A MODERATE TO ELEVATED RISK FOR SEVERE STORMS AND
SMALL HAIL. FROM TUESDAY ONWARD...THERE IS STILL A RISK FOR
ISOLATED TO SCATTERED THUNDERSTORMS IN AREAS OF
CONVERGENCE...PARTICULARLY ACROSS WESTERN PR IN THE
AFTERNOONS...WITH ISOLATED THUNDERSTORM RISK OVER EASTERN PR AND
THE USVI.

ALAMO...WPC (USA)