Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 040958
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
558 AM AST FRI SEP 4 2015

.SYNOPSIS...TUTT LOW OVER PUERTO RICO AND THE VIRGIN ISLANDS. A
MID LEVEL SHORT WAVE TROUGH EXTENDING ACROSS THE REGION AND WILL
SHIFT SLOWLY WESTWARD THROUGH SATURDAY...AS HIGH PRESSURE RIDGE
BUILDS OVER THE TROPICAL ATLANTIC. AN AMPLIFYING POLAR TROUGH
WILL EXIT THE EASTERN SEABOARD OF THE UNITED STATES AND SPREAD
EASTWARD OVER THE WESTERN ATLANTIC. THIS IN TURN WILL ERODE THE
UPPER RIDGE OVER THE WEST AND CENTRAL ATLANTIC NORTH OF THE REGION.
WEAK SURFACE HIGH PRESSURE RIDGE NORTH OF THE AREA WILL CONTINUE
TO LIFT NORTH AND EAST OF THE AREA TO MAINTAIN A LIGHT EASTERLY
TRADE WINDS TODAY AND INTO THE WEEKEND.

&&

.DISCUSSION...MID TO UPPER LEVEL TUTT LOW AND ASSOCIATED TROUGH
WILL CONTINUE TO WEAKEN THE CAP INVERSION. THIS WILL ALLOW FOR
BETTER LOW LEVEL INSTABILITY AND MIXING AS WELL AS BETTER SEA
BREEZE CONVERGENCE TODAY AND SATURDAY. AVAILABLE MOISTURE ACROSS
THE REGION...ALONG WITH LOCAL AND DIURNAL EFFECTS WILL AID IN
AFTERNOON CONVECTIVE DEVELOPMENT MAINLY ACROSS PARTS OF PUERTO
RICO. SOME ENHANCED CONVECTION WILL AGAIN REMAIN POSSIBLE TODAY
MAINLY OVER THE PORTIONS OF WESTERN PUERTO RICO. HOWEVER...THE
AFTERNOON CONVECTION IS NOT EXPECTED TO BE AS INTENSE AS THE
PREVIOUS DAY...AS THE MID LEVEL SHORT WAVE TROUGH AND ASSOCIATED
VORTICITY MAXIMA IS EXPECTED TO SHIFT FARTHER WEST ACROSS THE MONA
PASSAGES BY MID DAY TODAY.

THE TUTT WILL CONTINUE TO SHIFT FARTHER WEST OF THE ISLANDS WHILE
WEAKENING OVER THE NEXT FEW DAYS. AS THIS FEATURE WEAKENS...MID TO
UPPER LEVEL RIDGE WILL THEN SLOWLY BUILD ACROSS THE FORECAST AREA...
AND HOLD THROUGH AT LEAST THE MIDDLE OF NEXT WEEK. A WEAK TROPICAL
WAVE IS STILL FORECAST TO MOVE ACROSS THE REGION LATE SUNDAY OR MONDAY...
BUT NO SIGNIFICANT MOISTURE ADVECTION OR UPPER LEVEL SUPPORT IS SUGGESTED
AT THIS TIME. DURING THE LATTER PART OF THE FORECAST PERIOD ANOTHER
ACTIVE TROPICAL WAVE IS FORECAST TO APPROACH THE REGION. THIS FEATURE
HOWEVER IS STILL SOME WAYS OUT...SO WILL HAVE TO MONITOR AND SEE HOLD
IT UNFOLDS AND THE MODEL GUIDANCE ADJUSTS WITH TIME.

&&

.AVIATION...MOSTLY VFR CONDITIONS EXPECTED ACROSS THE LOCAL
FLYING AREA THROUGH 04/16Z. LIGHT AND VARIABLE WINDS THROUGH
04/13Z...BECOMING EASTERLY WITH SEA BREEZE VARIATIONS THEREAFTER.
+TSRA EXPECTED ACROSS INTERIOR AND WESTERN PORTIONS OF PUERTO
RICO...AFTER 04/16Z WHICH WILL CAUSE MTN OBSCURATIONS AND LIKELY
AFFECT TJBQ AND TJMZ. VICINITY SHRA/TSRA ACROSS TJSJ AND TJBQ.
WEATHER CONDITIONS IMPROVING AFTER 04/23Z...LEAVING VFR CONDITIONS
AND LIGHT WINDS ONCE AGAIN

&&

.MARINE...LIGHT TO GENTLE WINDS OF LESS THAN 15 KNOTS TODAY WITH
SEAS OF 3 FEET OR LESS. EXPECT THESE CONDITIONS TO CONTINUE THROUGH
THE WEEKEND AND INTO EARLY NEXT WEEK. THERE ARE NO MARINE PRECAUTIONARY
STATEMENTS OR ADVISORIES IN EFFECT AT THIS TIME.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  92  79  91  79 /  20  30  30  30
STT  89  80  89  79 /  20  40  40  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...NONE.
VI...NONE.
AM...NONE.
&&

$$

72/09


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