Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 310229
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1029 PM AST THU OCT 30 2014

.UPDATE...WEAK LOW PRESSURE NORTHEAST OF PUERTO RICO IS ENHANCING
THE LOW LEVEL CONVERGENCE ACROSS LOCAL REGION. IN ADDITION...A
SHORT-WAVE TROUGH ALOFT HAS PROVIDED ADDITIONAL INSTABILITY ACROSS
THE ISLANDS TO SUPPORT THE DEVELOPMENT OF STRONG THUNDERSTORMS
WITH HEAVY RAINFALL AND FREQUENT LIGHTNING OVER PR THIS EVENING.
RAINFALL ACCUMULATIONS SINCE NOON TODAY HAVE GENERALLY RANGED
BETWEEN 1-3 INCHES IN PORTIONS OF THE SAN JUAN METRO AREA AND
NORTH CENTRAL PR. ISOLATED SPOTS OF 3-4 INCHES HAVE BEEN ESTIMATING
BY THE DOPPLER RADAR IN SAN JUAN...CIALES AND TOA ALTA. THE WEAK
SURFACE LOW IS EXPECTED TO DISSIPATE OVER THE NEXT 12-24 HRS AS
MOVES TO THE NNW OVER THE WESTERN ATLANTIC. THE TROUGH ALOFT WILL
MOVE EASTWARD OVER THE LESSER ANTILLES ON FRIDAY. THEREFORE...WEATHER
CONDITIONS WILL GRADUALLY IMPROVE DURING OVERNIGHT HOURS AND FRIDAY
AS UPPER RIDGE ESTABLISH ACROSS THE NORTHEAST CARIBBEAN ISLANDS.
NO CHANGES WERE INTRODUCED TO THE FORECAST PACKAGE THIS EVENING.

&&

.AVIATION...TEMPO MVFR CONDS WITH VCTS/VCSH EXPECTED AT TJSJ...
TJBQ...TISX AND TIST TIL 31/03Z. SCT-BKN LOW TO MID LVL CLDS BTW
FL018-FL120 WITH SCT HIGH LVL CLOUDS MAINLY DUE TO BLOW OFF FM
CONVECTIVE ACTIVITY ACROSS NRN PR AND BTW ERN PR AND THE VIRGIN
ISLANDS. ISLD TSTMS ALONG N COAST OF PR AND EN ROUTE BTW ERN PR
AND THE NRN LEEWARDS WITH MAX TOPS NEAR FL400. MVFR/IFR CONDS FCST
IN VCTY OF CONVECTIVE ACTIVITY. MTN TOP OBSCR ALONG CENTRAL MTN
RANGE OF PR DUE TO LOW SCUD CLDS AND VCSH TIL AT LEAST 31/06Z.
THEREAFTER MOSTLY VFR CONDS OVER LAND AND AT ALL TAF SITES FOR
REST OF PRD. LGT/VRB SLY WNDS BLO FL200 THEN INCR W/HT ABV BCMG FM
NW 15-25 KTS UP TO FL450.

&&

.MARINE...SEAS WILL RANGE BETWEEN 2-4 FT UNTIL SUNDAY. THEN...
LONG PERIOD NW SWELLS WILL IMPACT THE ATLANTIC WATERS AND PASSAGES
EARLY NEXT WEEK...WAVE HEIGHT WILL RANGE BETWEEN 5-7 FT FROM MONDAY
THROUGH AT LEAST WEDNESDAY. DANGEROUS RIP CURRENTS WILL BE LIKELY
EARLY NEXT WEEK ACROSS THE NORTH FACING COASTLINES OF PR AND USVI.


&&

.PREV DISCUSSION... /ISSUED 232 PM AST THU OCT 30 2014/

SYNOPSIS...WEAK LOW PRESSURE WILL CONTINUE MOVING TO THE
NORTHWEST AND STAY TO THE NORTHEAST OF THE LOCAL AREA. UPPER
TROUGH WILL REMAIN OVER THE LOCAL AREA TODAY...LIFTING ON FRIDAY.
UPPER RIDGE WILL BUILD/EXPAND OVER THE AREA DURING THE
WEEKEND...LIMITING THE STRONG CONVECTION ACROSS THE ISLANDS.

DISCUSSION...SHOWERS DEVELOPED LATE THIS MORNING OVER THE
SOUTHERN SLOPES OF PUERTO RICO AS THE MEAN WIND FLOW WAS MAINLY
FROM THE NORTH. LATER...WIND SHIFTED TO A SOUTH TO SOUTHWESTERLY
DIRECTION EARLY IN THE AFTERNOON. THEN...SHOWERS AND THUNDERSTORMS
BEGAN TO DEVELOPED OVER THE CORDILLERA CENTRAL OF PUERTO RICO.
THESE SHOWERS AND THUNDERSTORMS WERE MOVING NORTH NORTHEAST. THE
SHIFT IN WIND DIRECTION WAS PRODUCE BY THE CIRCULATION ASSOCIATED
WITH AN AREA OF LOW PRESSURE WHICH WAS LOCATED FEW HUNDRED MILES
NORTHEAST OF PUERTO RICO. THIS AREA OF LOW PRESSURE WILL CONTINUE
TO MOVE NORTHWEST AWAY FROM THE AREA. THEREFORE...A SOUTH TO
SOUTHEAST WIND FLOW IS THEN EXPECTED TO PREVAIL THROUGH AT LEAST
SUNDAY...WHEN A RETURN TO A MORE EASTERLY WIND IS EXPECTED.

UPPER LEVEL RIDGE WILL BUILD ACROSS THE REGION DURING THE WEEKEND.
THEREFORE...ONLY LIGHT PASSING SHOWERS ARE EXPECTED DURING THE
WEEKEND MAINLY DURING THE MORNING HOURS...WITH SHOWERS AND
POSSIBLE THUNDERSTORMS EXPECTED TO DEVELOP OVER THE CORDILLERA
CENTRAL OF PUERTO RICO DUE TO DIURNAL HEATING AND LOCAL EFFECTS.

AVIATION...SHOWERS AND A FEW THUNDERSTORMS WILL AFFECT THE NORTHERN
SECTIONS OF PUERTO RICO PRODUCING PERIODS OF MVFR OR EVEN IFR
CONDITIONS AND MOUNTAIN OBSCURATIONS ACROSS TJSJ...TJBQ AND TJMZ
UNTIL AT LEAST 30/22Z. AFTER THAT MOSTLY VFR CONDITIONS ARE EXPECTED
ACROSS THE LOCAL FLYING AREA WITH VICINITY SHOWERS.

MARINE...SEAS UP TO 4 FEET AND WINDS UP TO 17 KNOTS ARE EXPECTED
OVER THE COASTAL WATERS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  77  88  77  89 /  60  50  20  20
STT  78  88  79  89 /  50  50  30  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
COASTAL WATERS...NONE.
&&

$$

09/11






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