Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 281905
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
305 PM AST TUE JUL 28 2015

.SYNOPSIS...
TUTT LOW NOW CENTERED OVER THE NORTHERN LEEWARDS WILL CONTINUE TO RETROGRESS
OVER THE REGION DURING THE NEXT FEW DAYS. MID LEVEL HIGH PRESSURE RIDGE
WILL HOWEVER LINGER JUST NORTH OF THE REGION AT LEAST UNTIL WEDNESDAY...WHEN
IT IS THEN FORECAST TO ERODE. SURFACE HIGH PRESSURE WILL REMAIN IN PLACE
ACROSS THE SOUTHWEST AND CENTRAL ATLANTIC. THIS WILL MAINTAIN MODERATE
TO STRONG EASTERLY TRADE WINDS ACROSS THE REGION FOR THE REMAINDER
OF THE WEEK. A TROPICAL WAVE IS FORECAST TO ENTER THE EASTERN CARIBBEAN
BY WEDNESDAY. IT IS TO THEN MOVE ACROSS THE REGIONAL WATERS ON THURSDAY
AND FRIDAY...WHILE TRANSPORTING A SURGE OF TROPICAL MOISTURE. THIS
EXPECTED OVERALL PATTERN WILL INCREASE THE CHANCE FOR SHOWERS AND
THUNDERSTORM ACROSS THE ISLANDS AND LOCAL WATERS... WITH POTENTIAL
FOR PERIODS OF MODERATE TO HEAVY RAINFALL AT TIMES IN ISOLATED AREAS.

&&
.DISCUSSION...MID TO UPPER LEVEL RIDGING WILL CONTINUE TO HELP
LIMIT CONVECTIVE DEVELOPMENT TODAY THROUGH WEDNESDAY...EXCEPT FOR
PARTS OF WEST PR WHERE LOCAL FORCING AND DIURNAL EFFECTS MAY LEAD
TO SOME SHOWER DEVELOPMENT ACROSS PARTS OF THE INTERIOR SECTIONS
OF PUERTO RICO LATE IN THE AFTERNOON OR EARLY EVENING. THE PREVAILING
LOW LEVEL EASTERLIES WILL HOWEVER CONTINUE TO SPREAD THE SAHARAN AIR
LAYER ACROSS THE REGION AND THEREFORE BRING HOT AND OVERAL DRY AND
HAZY CONDITIONS DUE TO THE SUSPENDED DUST PATRTCULATES. THIS WILL
CONTINUE TO SUPPRESS SIGNIFICANT SHOWER DEVELOPMENT AT LEAST
UNTIL LATE WEDNESDAY.

BY WEDNESDAY...THE TUTT LOW IS FORECAST TO RELOCATE OVERHEAD
WHILE MID LEVEL RIDGE ERODES. THIS WILL ALLOW FOR MORE MOISTURE
ADVECTION AND POOLING ACROSS THE REGION AS THE NEXT TROPICAL WAVE
AND ASSOCIATED TROPICAL MOISTURE CROSSES THURSDAY THROUGH FRIDAY.
RECENT MODEL GUIDANCE...ALL SUGGEST INCREASING MOISTURE WITH BETTER
POTENTIAL FOR SHOWERS AND THUNDERSTORMS ACROSS THE ISLANDS AND
SURROUNDING WATERS AS THESE TWO FEATURES INTERACT. BY THE WEEKEND
HOWEVER...LESSER ACTIVITY AND DECREASING MOISTURE TRANSPORT IS
EXPECTED...AS TUTT SHIFTS FARTHER WEST AND WEAKENS...AND THE
SURFACE HIGH REESTABLISHES ACROSS THE NORTHEASTERN CARIBBEAN.

&&

.AVIATION...VFR CONDS EXPECTED THROUGH THE FORECAST PERIOD.
VCSH/VCTS POSSIBLE ACROSS TJMZ AFTER 28/17Z. SAHARAN DUST PRESENT
CAUSING HAZE BUT VISIBILITY EXPECTED TO REMAIN P6SM. WINDS FROM THE
EAST WITH SEA BREEZE VARIATIONS AT 15-20 KNOTS AND GUSTY FOR THE
REST OF TODAY...DIMINISHING AFTER 29/00Z TO 5-10 KTS...INCREASING
ONCE AGAIN TO AROUND 15 KTS AFTER 29/13Z.

&&

.MARINE...SMALL CRAFT SHOULD CONTINUE TO EXERCISE CAUTION AS SEAS
WILL BE UP TO 6 FEET AND WINDS UP TO 20 KNOTS. PLEASE REFER TO THE
LATEST COASTAL WATERS FORECAST ISSUED BY THE NATIONAL WEATHER SERVICE
WFO SAN JUAN PR.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  79  91  79  91 /  20  20  10  30
STT  79  90  79  90 /  20  30  30  30

&&

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

$$

25/09


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