642
FXCA62 TJSJ 190915
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
515 AM AST SUN MAY 19 2019
SYNOPSIS
A SURGE IN LOW LEVEL MOISTURE WILL INCREASE SHOWERS
ACROSS THE USVI AND EASTERN PR LATER TODAY AND THROUGH THE
OVERNIGHT HOURS. SHOWERS AND THUNDERSTORMS ARE EXPECTED EACH AFTERNOON
MAINLY ACROSS THE NORTHWEST QUADRANT OF PUERTO RICO FOR THE NEXT
SEVERAL DAYS. ELSEWHERE, SCATTERED SHOWERS ARE POSSIBLE AND
ISOLATED THUNDERSTORMS CAN NOT BE RULED OUT. AN UPPER LEVEL
TROUGH WILL CONTINUE TO APPROACH THE FORECAST AREA FROM THE
NORTHWEST AND MOVE JUST NORTH OF THE REGION BY THURSDAY. LIGHT TO
MODERATE SOUTHEASTERLY TRADES WILL CONTINUE ACROSS THE REGION
THROUGH NEXT WEEK.
SHORT TERM...SUNDAY THROUGH TUESDAY
A MID TO UPPER-LEVEL TROUGH CURRENTLY NORTHWEST OF PUERTO RICO WILL
CONTINUE TO MOVE TO THE EAST OVER THE NEXT SEVERAL DAYS. AS THE MID
TO UPPER-LEVEL TROUGH MOVES CLOSER IT WILL WEAKEN THE MID TO UPPER-
LEVEL RIDGE, AND CAUSE THE RIDGES TO GRADUALLY MOVE TO THE EAST. AT
THE LOW-LEVELS A SURFACE HIGH OVER THE EASTERN ATLANTIC AND TROUGH
350 MILES NORTH OF PUERTO RICO WILL INDUCE AN EAST TO SOUTHEAST
WINDS OVER THE REGION. ALSO, AN INCREASE LOW-LEVEL MOISTURE OVER THE
NEXT SEVERAL DAYS ACROSS PUERTO RICO AND THE LOCAL WATERS.
AN INCREASE IN SHOWERS AND ISOLATED THUNDERSTORMS ARE FORECAST TO
DEVELOP ACROSS NORTHWESTERN AREAS OF PUERTO RICO. AS A RESULT OF
SIGNIFICANT SURFACE HEATING COMBINED WITH LOCAL AND DIURNAL EFFECTS.
IN ADDITION, DUE TO PROXIMITY OF THE MID TO UPPER-LEVEL TROUGH AND
SUB-TROPICAL JET A SLIGHT INCREASE IN UPPER-LEVEL DIVERGENCE IS
EXPECTED MAINLY ACROSS NORTHWESTERN AREAS OF PUERTO RICO DURING THE
AFTERNOON.
THEREFORE, DURING THE REST OF OF THE SHORT-TERM PERIOD
SHOWERS WILL MATURE TO THUNDERSTORMS ACROSS INTERIOR AND WESTERN
AREAS OF PUERTO RICO. THESE SHOWERS COULD CAUSE URBAN AND SMALL
STREAM FLOODING AND PONDING OF WATER ON ROADWAYS. ELSEWHERE,
ISOLATED TO SCATTERED SHOWERS ARE POSSIBLE ACROSS THE U.S. VIRGIN
ISLANDS, INTERIOR, AND EASTERN AREAS OF PUERTO RICO DURING THE EARLY
MORNING AND AFTERNOON.
LONG TERM...WEDNESDAY THROUGH SUNDAY
A MID TO UPPER LEVEL TROUGH IS FORECAST TO MOVE FROM THE WESTERN
ATLANTIC AND OVER THE NORTHEASTERN CARIBBEAN BETWEEN WEDNESDAY AND
THURSDAY. THIS WILL PROVIDE UPPER LEVEL SUPPORT FOR THE
DEVELOPMENT OF SHOWERS AND THUNDERSTORMS ACROSS PR AND PORTIONS OF
THE USVI. PRECIPITABLE WATER CONTENT IS FORECAST TO PEAK DURING
THIS PERIOD BETWEEN 1.75-2.00 INCHES, THEREFORE THE POTENTIAL FOR
FLOODING RAINS WILL BE HIGH.
ANOTHER SHORT WAVE TROUGH IS FORECAST TO MOVE JUST NORTHEAST OF
THE REGION DURING THE WEEKEND. THIS WILL CONTINUE TO PROVIDE
DIVERGENCE ALOFT TO SUPPORT AFTERNOON CONVECTION. AT LOWER LEVELS,
THE ABSENCE OF THE TRADE WIND CAP AND LIGHT SOUTHERLY STEERING
WINDS WILL ALLOW FOR TROPICAL MOISTURE TO POOL OVER THE REGION.
INDUCED PERTURBATIONS ACROSS THE EASTERN CARIBBEAN IN COMBINATION
WITH TROUGH PATTERN ALOFT WILL INCREASE THE POTENTIAL FOR SHOWER
ACTIVITY WITH POSSIBLE THUNDERSTORMS ACROSS THE CARIBBEAN WATERS
AND ACROSS THE USVI/EASTERN SECTIONS OF PR LATE IN THE WEEKEND.
AVIATION
VFR CONDS EXPECTED THROUGH THE FORECAST PERIOD WITH
VCSH/VCTS AT TJMZ AND TJBQ BY 19/18Z. THEN SHRA/VCTS SHOULD END BY
20/01Z WITH SCT TO BKN SKIES. WINDS WILL BE OUT OF THE EAST TO
SOUTHEAST AT 10 TO 15 KTS WITH HIGHER GUSTS POSSIBLE.
MARINE
SEAS ARE EXPECTED TO RANGE BETWEEN 3-5 FEET IN GENERAL
WITH THE HIGHEST SEAS EXPECTED ACROSS THE ATLANTIC WATERS. EAST TO
SOUTHEAST WINDS WILL PREVAIL BETWEEN 5-15 KTS WITH SEA BREEZE
INFLUENCES AFTER 10 AM EACH DAY. A MODERATE RISK OF RIP CURRENTS
WILL CONTINUE FOR THE NORTHERN BEACHES OF PUERTO RICO AND ST.
THOMAS.
PRELIMINARY POINT TEMPS/POPS
SJU 90 78 89 77 / 30 40 30 30
STT 86 77 86 77 / 40 30 30 50
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM...TW
LONG TERM....DS
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