Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 221535
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1135 AM AST WED OCT 22 2014

.UPDATE...NO SIGNIFICANT CHANGES FROM PREVIOUS DISCUSSION. LATEST
GUIDANCE AND CURRENT OBSERVATIONS ARE IN AGREEMENT WITH THE
INHERITED FORECAST. THE DEVELOPMENT OF SHOWERS AND ISOLATED
THUNDERSTORMS IN THE AFTERNOON ARE EXPECTED MAINLY IN THE
WEST AND NORTHWESTERN SECTIONS OF PR.

VISIBLE SATELLITE SHOWS CLOUDINESS INCREASING ACROSS THE LOCAL
AREA DUE TO OROGRAPHIC LIFTING...CAUSING CLOUDS TO STREAM OFF THE
USVI...VIEQUES AND CULEBRA. HOWEVER THE WESTERN AND NORTHWESTERN
SECTIONS OF PR SHOULD DEVELOP CLOUDINESS JUST AROUND NOON...AS THE
SEA BREEZE CONVERGENCE ALSO PLAYS A ROLE. OTHER THAN THAT...ONLY
PASSING SHOWERS ARE POSSIBLE OR EXPECTED ELSEWHERE.


&&

.AVIATION...NO CHANGES FROM PREVIOUS DISCUSSION. VCTS FOR TJBQ AND
TJMZ IN THE AFTERNOON. TEMPO GROUPS NOT PRESENT AT THIS TIME DUE
TO SOME UNCERTAINTY ON TIMING AND EXACT LOCATION...BUT TSRA IS
EXPECTED IN THE AREA. ALSO...CURRENT WEATHER IS CONDUCIVE FOR FAIR
WEATHER WATERSPOUTS IN THE LOCAL FLYING AREA. WX CONDS EXPECTED TO
IMPROVE THIS EVENING. CURRENT WINDS PREVAILING FROM THE EAST TO
E-SE AT 10-15 KTS...DIMINISHING OVERNIGHT TO 5-10 KTS.


&&

.MARINE...SEAS 2-4 FEET AND WINDS 15 KNOTS OR LESS CAN BE EXPECTED
ACROSS THE REGIONAL WATERS OVER THE NEXT FEW DAYS.


&&

.PREV DISCUSSION... /ISSUED 508 AM AST WED OCT 22 2014/

SYNOPSIS...UPPER TROUGH EXTENDING FROM THE CENTRAL ATLANTIC
SOUTHWEST INTO THE LEEWARD ISLANDS WILL REMAIN EAST OF THE LOCAL
AREA OVER THE NEXT FEW DAYS. MID LEVEL RIDGE WILL HOLD ACROSS THE
EAST AND CENTRAL CARIBBEAN THROUGH THE END OF THE WEEK. THE TROUGH
ALOFT EAST OF THE AREA WILL COMBINE WITH THE MID LEVEL RIDGE TO
FAVOR A SUBSIDENCE PATTERN ACROSS THE LOCAL REGION THROUGH AT
LEAST SUNDAY. A TROPICAL WAVE WILL MOVE ACROSS THE EASTERN CARIBBEAN
REGION ON FRIDAY...HOWEVER THE BULK OF THE MOISTURE WILL REMAIN
OVER THE CARIBBEAN WATERS.

DISCUSSION...TROUGHINESS ALOFT JUST EAST OF THE FORECAST AREA
HAS ENHANCED THE TRADE WIND SHOWERS ACROSS THE LOCAL CARIBBEAN
WATERS SINCE MIDNIGHT. DOPPLER RADAR SHOWED SCATTERED SHOWERS
MOVING EASTWARD ACROSS THE REGIONAL WATERS EARLY THIS MORNING.
THIS ACTIVITY IS EXPECTED TO DIMINISH LATER THIS MORNING AS UPPER
TROUGH SETTLES OVER LEEWARD ISLANDS. GFS ENSEMBLE SUGGEST THAT THE
OVERALL MOISTURE WILL DECREASE AS THE AFOREMENTIONED MID LEVEL
RIDGE BUILD ACROSS THE NORTHEAST CARIBBEAN ISLANDS. THIS RIDGE
WILL INDUCE A SUBSIDENCE INVERSION OVER THE LOCAL ISLANDS...
ALLOWING THE GRADUAL EROSION OF AVAILABLE MOISTURE. ANY CONVECTION
THAT DEVELOPS THIS AFTERNOON WILL BE MOSTLY SHALLOW UNDER THE
INFLUENCE OF THE MID LEVEL RIDGE.

THE TROPICAL WAVE NEAR 56 WEST THIS MORNING IS FORECAST TO ENTER
INTO THE EASTERN CARIBBEAN REGION LATE TONIGHT INTO THURSDAY
MORNING. OPERATIONAL MODELS SUGGEST THAT THE WAVE WILL ENCOUNTER
UNFAVORABLE CONDITIONS ALOFT INDUCED BY THE MID-LEVEL RIDGE OVER
THE EASTERN CARIBBEAN. THIS WILL RESULT IN LESS CONVECTION AFFECTING
THE LOCAL REGION FRIDAY AND SATURDAY. IN ADDITION...THE LATEST
GFS GUIDANCE SUGGEST THAT THE BEST MOISTURE CONVERGE ASSOCIATED
WITH THE WAVE WILL REMAIN OVER THE CARIBBEAN WATERS. IN GENERAL...
FAIR WEATHER SHOULD PREVAIL ACROSS THE LOCAL ISLANDS THROUGH THE
END OF THE WEEKEND...WITH SOME SHALLOW CONVECTION DEVELOPING OVER
WESTERN PR EACH AFTERNOON.

AVIATION...MOSTLY VFR CONDITIONS WILL PREVAIL THRU THE FORECAST
PERIOD WITH POSSIBLE VCTS NEAR TJMZ AND TJBQ BETWEEN 17Z-21Z.
EASTERLY WIND FLOW OF 5-15 KT CAN BE EXPECTED BELOW 10K FEET.

MARINE...SEAS 2-4 FEET AND WINDS 15 KNOTS OR LESS CAN BE EXPECTED
ACROSS THE REGIONAL WATERS OVER THE NEXT FEW DAYS. PULSES OF A SMALL
NORTHERLY SWELL WILL CONTINUE TO REACH THE LOCAL ATLANTIC WATERS
AND PASSAGES THROUGH THE END OF THE WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  90  77  92  77 /  20  10  20  40
STT  88  78  89  79 /  20  20  20  40

&&

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

$$

25/09





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