Prognostic Meteorological Discussion
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TROPICAL DISCUSSION - INTERNATIONAL DESKS
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
659 AM EDT WED JUL 26 2017


PRELIMINARY DISCUSSION FOR PUERTO RICO AND THE USVI FROM JULY
26/06 UTC: A RETROGRESSING TUTT LOW NEAR 27N 57W EXTENDS A TROUGH
TO THE SOUTH-SOUTHWEST TO THE NORTHEASTERN CARIBBEAN. THIS IS
PRESSING AGAINST WANING CELL OF THE SUBTROPICAL RIDGE OVER THE
WESTERN ATLANTIC/NORTH OF THE ISLANDS...FAVORING EROSION OF MID
LEVEL RIDGE PATTERN. AS THE RIDGE WEAKENS AND THE TRADE WINDS CAP
LIFTS...DEEPER CONVECTIVE INSTABILITY IS ENVELOPING THE FORECAST
AREA. THIS...IN-TURN...IS ALLOWING A DEEP PLUME OF TROPICAL
MOISTURE TO ADVECT ACROSS THE FORECAST AREA IN ASSOCIATION WITH A
LOW/MID LEVEL TUTT INDUCED PERTURBATION PULLING ACROSS PUERTO
RICO. EARLY THIS MORNING THIS WILL SUSTAIN SCATTERED CONVECTION
ACROSS THE VIRGIN ISLES-EASTERN PUERTO RICO/SAN JUAN METRO
AREA...MEANWHILE FAVORING RAINFALL AMOUNTS OF 0.25-0.50 OF AN
INCH. MOST ACTIVE IS EXPECTED LATER IN THE MORNING/EARLY IN THE
AFTERNOON TO CLUSTER ACROSS NORTHWEST PUERTO RICO...BETWEEN
BARCELONETA/ARECIBO AND ISABELA. RAINFALL MAXIMA IN THIS AREA WILL
RANGE BETWEEN 2-4 INCHES. ON THURSDAY...MEANDERING TUTT IS
EXPECTED TO CONTINUE ENHANCING DIURNAL CONVECTION ACROSS THE
FORECAST AREA. MOST ACTIVE IS EXPECTED OVER SAINT CROIX IN EARLY
AFTERNOON CONVECTION AND WESTERN INTERIOR PORTIONS OF PUERTO RICO.

LATER IN THE WEEK...ANOTHER TUTT INDUCED PERTURBATION REACHES THE
FORECAST AREA EARLY ON FRIDAY MORNING. HOWEVER...DURING THIS
PERIOD THE TUTT PATTERN ALOFT WILL START TO RAPIDLY WANE. AS THE
UPPER SUPPORT WEAKENS...THE WAVE WILL NOT BE AS ACTIVE AS THE ONE
TODAY. BUT...NEVERTHELESS...IT SHOULD ENHANCE DIURNAL CONVECTION
AS IT STREAMS ACROSS PUERTO RICO DURING THE MORNING/EARLY
AFTERNOON HOURS...WITH MAXIMA OVER WESTERN INTERIOR PORTIONS OF
PUERTO RICO EXPECTED TO PEAK AT 1-2 INCHES.

AS THE TUTT PATTERN ALOFT WEAKENS...MID LEVEL RIDGE IS TO THEN
BOUNCE BACK. AS IT BUILDS ACROSS THE NORTHEAST CARIBBEAN ISLES
THIS IS TO THEN ESTABLISH AN UPPER LEVEL INVERSION THAT IS TO
INHIBIT ORGANIZED DEEP CONVECTION. IN THIS PATTERN A TROPICAL WAVE
REACHES THE ISLAND CHAIN LATER ON SUNDAY...AND THROUGH THE MORNING
HOURS ON MONDAY IT IS TO QUICKLY PULL ACROSS THE FORECAST AREA.
SINCE THIS IS MAKING LANDFALL DURING THE EARLY MORNING HOURS...AND
ENVIRONMENTAL CONDITIONS ARE TO BECOME SOMEWHAT HOSTILE TO
ORGANIZED DEEP CONVECTION...THE MOST ACTIVE CONVECTION WITH THIS
FEATURE IS EXPECTED OVER THE VIRGIN ISLES/EASTERN PUERTO RICO AND
CARIBBEAN/ATLANTIC COASTAL WATERS OF PUERTO RICO. IN THIS AREA
SCATTERED RAIN SHOWERS WILL LEAD TO RAINFALL AMOUNTS OF 0.25-0.50
OF AN INCH. PER THE METEOSAT DUST PRODUCT IT LOOKS LIKE A DRYER
SAHARAN AIR LAYER WILL THEN MOVE IN BEHIND THIS WAVE...TO LIKELY
FAVOR FAIR WEATHER CONDITIONS.

GAJADHAR...SLMS (SAINT LUCIA)
DAVISON...WPC (USA)
$$





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