Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 280220
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
1020 PM AST MON JUL 27 2015

.UPDATE...AFTER SHOWER ACTIVITY DIMINISHED OVER WESTERN BY 4 PM
AST...MOSTLY HAZY SKIES WITH A FEW CLOUDS WERE OBSERVED AND ARE
EXPECTED TO CONTINUE DURING THE OVERNIGHT HOURS. HIGH CIRRUS
CLOUDS ASSOCIATED WITH AN UPPER LEVEL LOW NORTHEAST OF THE AREA
WILL MOVE OVER THE ISLANDS THROUGH AT LEAST WEDNESDAY AS UPPER
LOW MOVES TOWARDS THE MONA PASSAGE ACROSS THE ATLANTIC WATERS.
SAHARAN AIR LAYER WILL WILL PERSIST THROUGH AT LEAST THURSDAY BUT
WILL RETURN BY LATE FRIDAY AND INTO THE WEEKEND. OVERALL...MID
LEVEL DRY AIR AND TRADE WIND CAP WILL LIMIT SHOWER ACTIVITY ACROSS
THE FORECAST AREA...WITH THE EXCEPTION OF AFTERNOON SHOWERS OVER
WESTERN PR. LIMITED RAINFALL IS FORECAST ACROSS THE U.S. VIRGIN
ISLANDS AND SECTIONS OF EASTERN PR DURING THE NEXT COUPLE OF DAYS.
BEST CHANCE FOR SHOWERS STILL HOLDS FOR THURSDAY WHEN A WEAK
TROPICAL WAVE AND UPPER LEVEL LOW ARE FORECAST TO INTERACT WITH
EACH OTHER AND INCREASE MOISTURE AND INSTABILITY ACROSS THE
FORECAST AREA. MINOR CHANGES MADE TO SHORT TERM GRIDS.


&&


.AVIATION UPDATE...VFR CONDS EXPECTED AT ALL TAF SITES. SAHARAN
DUST PRESENT OVER THE AREA BUT VISIBILITY EXPECTED TO REMAIN P6SM.
SHRA/TSRA POSSIBLE IN AND AROUND TJMZ BETWEEN 28/17Z AND 28/22Z.
EASTERLY WINDS 10 KNOTS OR LESS OVERNIGHT...INCREASING AGAIN TO
AROUND 15 KNOTS AFTER 28/13Z.


&&


.MARINE UPDATE...AS OF 10 PM AST...BUOYS ACROSS THE LOCAL ISLANDS
WERE INDICATING SEAS OF 3-4 FEET AND EAST WINDS AROUND 15 KNOTS
WITH HIGHER GUSTS. HOWEVER...WIND PROTECTED COASTAL WATERS OF
WESTERN PR WERE 2 FEET OR LESS. SMALL CRAFT OPERATORS SHOULD
CONTINUE TO EXERCISE CAUTION ACROSS THE ATLANTIC AND CARIBBEAN
WATERS INCLUDING THE ANEGADA AND MONA PASSAGE AS BREEZY CONDITIONS
PREVAIL INTO TUESDAY MORNING AND SEAS UP TO 6 FEET ARE POSSIBLE
ACROSS THE OPEN OFFSHORE WATERS.


&&

.PREV DISCUSSION... /ISSUED 324 PM AST MON JUL 27 2015/

SYNOPSIS...A MID TO UPPER LEVEL RIDGE CONTINUED IN PLACE ACROSS THE
ATLANTIC AND WILL DOMINATE THE LOCAL WEATHER PATTERN AT LEAST THROUGH
TUESDAY. STRONG SURFACE HIGH PRESSURE WILL REMAIN IN PLACE ACROSS
THE SOUTHWEST AND CENTRAL ATLANTIC. THIS WILL HELP TO MAINTAIN MODERATE
EASTERLY TRADE WINDS ACROSS THE REGION FOR MOST OF THE WEEK. A TROPICAL
WAVE IS FORECAST TO ENTER THE EASTERN CARIBBEAN BY MID WEEK...THEN MOVE
ACROSS THE REGIONAL WATERS ON THURSDAY.

DISCUSSION...HOT AND HAZY CONDITIONS PREVAILED ACROSS THE REGION
TODAY WITH LIMITED SHOWERS ACTIVITY...AS A STRONG CAP INVERSION
AND AND THE PRESENCE OF SAHARAN DUST LIMITED CONVECTIVE DEVELOPMENT.
EXPECT MOSTLY CLEAR SKIES AND HAZY CONDITIONS DURING OVERNIGHT HOURS
AND ON TUESDAY. SOME LIGHT PASSING SHOWERS MAY MOVE ACROSS THE LOCAL
WATERS BUT NO SIGNIFICANT RAINFALL AMOUNTS ARE EXPECTED OVER LAND.

AT LEAST UNTIL WEDNESDAY AND THURSDAY...EXPECT FAIRLY DRY AND STABLE
CONDITIONS DUE TO THE MID TO UPPER LEVEL RIDGING... LIMITED MOISTURE
ADVECTION...AND THE PRESENCE OF SAHARAN DUST PARTICULATES.
AFTERNOON CONVECTION IF ANY WILL BE FOCUSED MAINLY OVER SECTIONS
OF WESTERN PUERTO RICO. LESSER CHANCE FOR SHOWERS EXPECTED OVER
THE VIRGIN ISLANDS ON TUESDAY.

BY WEDNESDAY...RIDGE ALOFT IS TO GRADUALLY ERODE AS AN UPPER LEVEL
LOW/TUTT WILL RELOCATE WESTWARD ACROSS THE REGION WEDNESDAY THROUGH
THURSDAY. LATEST SATELLITE IMAGERY AND NAAPS AEROSOL PRODUCT CONTINUED
TO SUGGEST THE SAHARAN AIR LAYER WAS NOW SPREAD ACROSS THE REGION...
WITH THE HIGHEST CONCENTRATION OF SUSPENDED SAHARAN DUST TO AFFECT
THE REGION TODAY THROUGH TUESDAY...THEN GRADUALLY DIMINISH BY MID
WEEK.

A TROPICAL WAVE IS EXPECTED TO REACH THE EASTERN CARIBBEAN LATE
WEDNESDAY...THEN MOVE ACROSS THE AREA ON THURSDAY. THIS ALONG WITH
THE REPOSITIONING OF THE TUTT LOW ALOFT WILL HELP CREATE UPPER LEVEL
INSTABILITY...AND THEREFORE INCREASE THE CHANCE FOR SHOWERS AND
THUNDERSTORMS DURING THE LATTER PART OF THE WORK WEEK. MODELS
HOWEVER STILL SUGGEST...DRIER CONDITIONS WILL QUICKLY RETURN BY
THE WEEKEND AS THE SAHARAN AIR LAYER WILL AGAIN MOVE OVER THE
REGION.

AVIATION...VFR CONDS EXPECTED ACROSS THE LOCAL TERMINALS. SHRA
EXPECTED IN AND AROUND TJMZ THROUGH 27/21Z. ONLY A SLIGHT CHANCE OF
BRIEF SHRA ACROSS THE LOCAL AREA OVERNIGHT...THEREFORE BRIEF VCSH IS
POSSIBLE ACROSS TIST/TISX AS WELL AS TJSJ. SUSPENDED SAHARAN DUST
PRESENT OVER THE AREA BUT VISIBILITY EXPECTED TO REMAIN P6SM.
EASTERLY WINDS WITH SEA BREEZE VARIATIONS AT AROUND 15-20 KTS AND
GUSTY THROUGH REST OF THE DAY...GRADUALLY DIMINISHING TO AROUND
5-10 KTS AFTER 28/00Z INTO THE OVERNIGHT HOURS. WINDS INCREASING
AGAIN TO AROUND 15 KNOTS AFTER 28/13Z.

MARINE...WINDS UP TO 20 KNOTS AND LOCAL SEAS UP TO 6 FEET. SMALL CRAFT
SHOULD EXERCISE CAUTION ACROSS MOST OF THE LOCAL WATERS OVERNIGHT
THROUGH TUESDAY.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  78  89  79  89 /  10  10  20  20
STT  80  90  79  89 /  20  20  20  20

&&

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

$$

23/13


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