889
FXCA62 TJSJ 230039
AFDSJU
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
839 PM AST THU AUG 22 2019
UPDATE
FORECAST REMAINS ON TRACK. LINGERING LOW-LEVEL MOISTURE
ASSOCIATED WITH A DEPARTING WEAK TROPICAL WAVE WILL PERSIST OVER
THE AREA THROUGH FRIDAY. THIS WILL RESULT IN SOME PASSING SHOWERS
ACROSS PORTIONS OF SOUTHEASTERN AND EASTERN PUERTO RICO AS WELL AS
ACROSS PORTIONS OF THE USVI DURING THE OVERNIGHT AND EARLY
MORNING HOURS OF FRIDAY. THEN, AS THE LOW-LEVEL MOISTURE COMBINES
WITH STRONG DAYTIME HEATING AND LOCAL EFFECTS, SCATTERED SHOWERS
AND ISOLATED THUNDERSTORMS WILL DEVELOP AND AFFECT PORTIONS OF
NORTHWEST PUERTO RICO AND POSSIBLY DOWNWIND OF THE USVI AND EL
YUNQUE, AFFECTING THE SAN JUAN METRO AREA, DURING THE EARLY TO
MID-AFTERNOON HOURS. GIVEN THAT THERE WILL BE A MID TO UPPER-LEVEL
RIDGE NEAR THE AREA, UPPER-LEVEL DYNAMICS ARE EXPECTED TO REMAIN
NON-EXISTENT. IN ADDITION, THE LOW-LEVEL FLOW WILL REMAIN PRETTY
FAST FROM THE EAST-SOUTHEAST BETWEEN 15 AND 20 KNOTS. THESE
FACTORS WILL LIMIT THE INTENSITY AS WELL AS THE DURATION OF THE
SHOWERS, THEREFORE, SIGNIFICANT RAINFALL ACCUMULATIONS ARE NOT
EXPECTED.
AVIATION
MAINLY VFR CONDITIONS ARE EXPECTED DURING THE FORECAST
PERIOD. VCSH EXPECTED ACROSS TJSJ/TISX/TIST/TNCM/TKPK. SCT
SHRA/TSRA EXPECTED ACROSS NORTHWEST PR BETWEEN 23/16Z AND 22/23Z,
AFFECTING THE VICINITY OF TJMZ/TJBQ. BRIEF MVFR CONDITIONS ARE
POSSIBLE. LIGHT AND VARIABLE WINDS OVERNIGHT, INCREASING TO 10 TO
20 KTS WITH HIGHER GUSTS FROM ESE WITH SEA BREEZE VARIATIONS
DEVELOPING AFTER 23/13Z.
MARINE
CHOPPY SEAS UP TO 6 FEET EXPECTED ACROSS THE ATLANTIC
WATERS, THEREFORE, SMALL CRAFT OPERATORS SHOULD EXERCISE CAUTION.
SEAS OF UP TO 5 FEET EXPECT ELSEWHERE. WINDS ARE EXPECTED TO RANGE
BETWEEN 10 AND 20 KNOTS FROM THE EAST. THERE IS A MODERATE RISK
OF RIP CURRENTS ACROSS THE NORTHERN AND SOUTHEASTERN BEACHES OF
PUERTO RICO AND ACROSS MOST OF THE BEACHES OF VIEQUES, CULEBRA,
AND SAINT CROIX THROUGH TONIGHT. IN ADDITION TO THESE
AFORMENTIONED AREAS, THE MODERATE RISK OF RIP CURRENTS WILL
EXTEND TO THE SOUTHWESTERN BEACHES OF PUERTO RICO AS WELL AS THE
NORTHWESTERN BEACHES OF SAINT THOMAS ON FRIDAY.
PREV DISCUSSION
/ISSUED 145 PM AST THU AUG 22 2019/
SYNOPSIS...PASSING TROPICAL WAVE AND ASSOCIATE PLUME OF MOISTURE
WILL AFFECT THE REGION THROUGH FRIDAY. RELATIVE STABLE CONDITIONS
ARE EXPECTED ON SATURDAY, BEFORE THE NEXT TROPICAL WAVE
APPROACHES THE REGION LATE SATURDAY NIGHT INTO SUNDAY. ALTHOUGH
THE ENTRANCE OF RELATIVELY DRIER AND STABLE AIR MASS ACCOMPANIED
BY SUSPENDED SAHARAN DUST WILL DOMINATE THE LOCAL AREA, LOCALLY
INDUCED SHOWERS ARE EXPECTED EACH AFTERNOON. LACK OF UPPER LEVEL
SUPPORT WILL LIMIT THUNDERSTORM DEVELOPMENT.
SHORT TERM...TONIGHT THROUGH SATURDAY...
REMNANTS FROM AFTERNOON SHOWER AND THUNDERSTORM ACTIVITY IS
EXPECTED TO LINGER ACROSS PORTIONS OF NORTHWESTERN PUERTO RICO AND
WATERS WEST OF PUERTO RICO THROUGH THE EVENING HOURS. DURING THE
OVERNIGHT AND EARLY MORNING HOURS, SHOWERS AND POSSIBLE ISOLATED
THUNDERSTORMS, ASSOCIATED TO A PASSING TROPICAL WAVE, ARE EXPECTED
TO AFFECT THE REGIONAL WATERS AND PORTIONS OF EASTERN PUERTO RICO
AND THE U.S. VIRGIN ISLANDS. AS THE DAY PROGRESSES, LOCALLY
INDUCED SHOWERS ARE EXPECTED TO DEVELOP OVER THE NORTHWESTERN
QUADRANT OF PUERTO RICO, AS WELL AS DOWNWIND FROM THE LOCAL
ISLANDS AND SIERRA DE LUQUILLO. ALTHOUGH UPPER LEVEL SUPPORT FOR
THUNDERSTORM DEVELOPMENT IS NOT EXPECTED, ISOLATED THUNDERSTORMS
CANNOT BE RULED OUT IN THE AFTERNOON. LOCALIZED URBAN AND SMALL
STREAM FLOODING POSSIBLE ACROSS THE NORTHWESTERN QUADRANT OF THE
ISLAND.
SOMEWHAT IMPROVED CONDITIONS ARE EXPECTED BETWEEN LATE FRIDAY
NIGHT INTO SATURDAY. HOWEVER, LOCALLY INDUCED SHOWERS ARE
POSSIBLE, PARTICULARLY DURING THE AFTERNOON HOURS. IF ANY, ABOVE-
NORMAL TEMPERATURES AND HEAT INDEX WILL BE A THREAT DURING THIS
PERIOD.
LONG TERM...SUNDAY THROUGH WEDNESDAY...
PREV DISCUSSION... /ISSUED 503 AM AST THU AUG 22 2019/
SUNDAY, RESIDUAL MOISTURE ASSOCIATED WITH A TROPICAL WAVE WILL LINGER
THROUGH THE EARLY AFTERNOON ON SUNDAY. THE MOISTURE COUPLED WITH
DAYTIME HEATING AND LOCAL EFFECTS WILL YIELD SHOWERS AND
THUNDERSTORMS DURING THE AFTERNOON ACROSS THE INTERIOR AND WESTERN
AREAS OF PUERTO RICO. THERE IS A POSSIBILITY FOR URBAN AND SMALL
STREAM FLOODING DURING THE AFTERNOON IN FLOOD PRONE AREAS. SUNDAY
EVENING THE MOISTURE WILL ABATE AS A DRY SAHARAN AIR MASS PUSH IN
FROM THE EAST ATLANTIC. THE DRY SAHARAN AIR IS FORECAST TO PERSIST
THROUGH EARLY PART OF THE NEXT WEEK. THEREFORE, EXPECT HAZY SKIES
WITH ISOLATED TO SCATTERED SHOWERS MAINLY DURING THE AFTERNOON WITH
THE CHANCE FOR ISOLATED THUNDERSTORMS OVER WESTERN PUERTO RICO. ONCE
AGAIN SHOWERS WILL DEVELOP DUE TO DAYTIME HEATING AND LOCAL EFFECTS.
HOWEVER, DUE TO MODEST LOW-LEVEL MOISTURE AND LIMITED UPPER-LEVEL
INSTABILITY AS A RESULT OF MID TO UPPER-LEVEL RIDGES SHOWERS WILL BE
SHORT-LIVED. BY TUESDAY THE 700 MB HIGH SHIFT TO THE SOUTHWEST THIS
SHIFT IN THE HIGH WILL ALLOW THE TROPICAL MOISTURE TO POOL INTO THE
REGION FROM THE EAST. THE RETURN OF THE DEEP TROPICAL MOISTURE WILL
CAUSE THE DRY SAHARAN AIR TO DIMINISH OVER THE REGION. ALSO, THE
TROPICAL MOISTURE WILL AID IN THE DEVELOPMENT OF SHOWERS AND
ISOLATED THUNDERSTORMS DURING THE AFTERNOON ESPECIALLY OVER AND
SOUTH OF THE CORDILLERA CENTRAL THROUGH THE MIDDLE OF THE WEEK.
AVIATION...BRIEF PERIODS OF MVFR CONDS WILL REMAIN POSSIBLE AT JBQ
IN SHRA/TSRA THROUGH ABOUT 22/22Z. AS THE TROPICAL WAVE MOVES AWAY
TONIGHT, CONDITIONS WILL IMPROVE WITH VCSH POSSIBLE AT THE LEEWARD
AND USVI TERMINALS OVERNIGHT. ESE WINDS AT 10 TO 15 KNOTS WITH SOME
SEA BREEZE VARIATIONS THROUGH 22/22Z BECOMING LIGHT AND VARIABLE
OVERNIGHT.
MARINE...CHOPPY MARINE CONDITIONS WITH SEAS UP TO 6 FEET AND
WINDS UP TO 20 KNOTS EXPECTED ACROSS THE ATLANTIC WATERS. THUS,
SMALL CRAFT OPERATORS SHOULD EXERCISE CAUTION ACROSS THESE AREAS.
ELSEWHERE, TRANQUIL MARINE CONDITIONS WITH SEAS UP TO 5 FEET AND
WINDS UP TO 15 KNOTS ARE EXPECTED TO PREVAIL. THERE IS A MODERATE
RISK OF RIP CURRENTS FOR THE NORTHERN AND SOUTHEASTERN BEACHES OF
PUERTO RICO, AS WELL AS MOST BEACHES OF VIEQUES, CULEBRA AND SAINT
CROIX.
PRELIMINARY POINT TEMPS/POPS
SJU 78 91 78 90 / 40 10 50 50
STT 80 91 80 88 / 40 30 40 40
SJU WATCHES/WARNINGS/ADVISORIES
PR...NONE.
VI...NONE.
AM...NONE.
SHORT TERM...GL
LONG TERM....WS
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