Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 041758
AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
158 PM AST WED MAY 4 2016

.SYNOPSIS...
MID TO UPPER TROUGH OVER THE NORTHEASTERN CARIBBEAN WILL CONTINUE
TO WEAKEN/FILL AND LIFT FARTHER EAST NORTHEAST OF THE FORECAST
AREA TODAY THROUGH EARLY THURSDAY. THIS WILL GIVE WAY TO A DEVELOPING
UPPER LEVEL RIDGE WHICH WILL PLACE THE REGION ON THE CONVERGENT/SUBSIDENT
SIDE OF THE UPPER TROUGH. LESS FAVORABLE CONDITIONS ALOFT FOR SIGNIFICANT
CONVECTIVE DEVELOPMENT CAN THEN BE EXPECTED ACROSS THE ISLANDS AND COASTAL
WATERS. HOWEVER...BY LATE THURSDAY AND THROUGH THE REST OF THE WEEK...THIS
RIDGE PATTERN IS TO ERODE IN RESPONSE TO A HIGH AMPLITUDE LONG WAVE
TROUGH DEEPENING ACROSS THE WEST AND SOUTHWEST ATLANTIC. THIS SYNOPTIC
PATTERN IS TO THEN HOLD IN PLACE THROUGH THE UPCOMING WEEKEND. LOW
LEVEL SUBTROPICAL RIDGE IS TO REMAIN ANCHORED ACROSS THE CENTRAL BUT
WILL BUILD AND SHIFT SLIGHTLY SOUTH AND EAST ACROSS THE ATLANTIC BY
FRIDAY AND INTO THE WEEKEND.

&&

.DISCUSSION...MODELS GUIDANCE CONTINUE TO SUGGEST THAT THE LONG
WAVE TROUGH WILL DEEPEN ACROSS THE WESTERN ATLANTIC AND SINK INTO
THE NORTHWEST CARIBBEAN THEN CONTINUE THROUGH THE WEEKEND. AS A
RESULT THE UPPER TROUGH IS FORECAST TO REMAIN JUST WEST OF THE
REGION FAVORING INCREASING INSTABILITY FOR FRIDAY AND INTO THE
WEEKEND. IN THE LOW LEVELS...THE DEEPENING POLAR TROUGH AND
ASSOCIATED COLD FRONT WILL MOVE ACROSS THE WESTERN ATLANTIC AND
SLOWLY LIFT EAST NORTHEAST RIDING THE PERIPHERY OF THE ATLANTIC
SUBTROPICAL RIDGE. THIS SURFACE HIGH WILL CONTINUE TO BUILD AND
REMAIN ANCHORED ACROSS THE CENTRAL AND EASTERN ATLANTIC THROUGH
THE WEEKEND. THIS PATTERN WILL SUPPORT INITIALLY A LOW LEVEL
SOUTHEAST WINDS THROUGH FRIDAY...THEN MODEL GUIDANCE SUGGEST LOW
LEVEL WINDS GRADUALLY VEERING AND BECOMING EVEN MORE SOUTHERLY
OVER THE WEEKEND.

BY THE WEEKEND THIS LOW LEVEL SOUTHERLY WIND FLOW WILL COMBINE
WITH INCREASING CAP INVERSION RESULTING IN WARMER SURFACE TEMPERATURES
ESPECIALLY ALONG THE NORTHERN HALF OF PUERTO RICO...WITH THE HOTTEST
DAY EXPECTED TO BE ON SATURDAY. WITH THAT SAID...FOR THE NEXT COUPLE
OF DAYS...EXPECT CONVECTIVE ACTIVITY TO BE LESSER ENHANCED AND SHOULD
BE FOCUSED OVER THE CENTRAL AND NORTHWEST SECTION OF PUERTO RICO.
THE PRESENT WIND FLOW WILL ALSO STEER SHOWERS OVER AND AROUND PARTS
OF THE SAN JUAN METRO AREA. INCREASING INSTABILITY ALOFT AND STRONG
TROPICAL MOISTURE CONVERGENCE BY FRIDAY AND INTO THE WEEKEND WILL
ALLOW BETTER CHANCE FOR ACTIVITY WEATHER CONDITIONS WITH MODELS CONTINUING
TO SUGGEST A FAIRLY WET PATTERN SUNDAY INTO MONDAY OF NEXT WEEK.

&&

.AVIATION...MVFR CONDS STILL PSBL AT TJMZ AND TJBQ IN PASSING TSRA
THRU 22Z. ALSO...SOME VCSH MAY AFFECT BRIEFLY TJSJ. VFR CONDS
EXPECTED ELSEWHERE. ESE WINDS OF 10-15 KT EXPECTED BELOW FL100.

&&

.MARINE...WINDS OF 5 TO 15 KNOTS WILL PREVAIL ACROSS THE REGIONAL
WATERS WITH SEAS OF 3 TO 5 FEET OVER THE NEXT SEVERAL DAYS. NO
SMALL CRAFT ADVISORIES ARE ANTICIPATED OVER THE NEXT 5-7 DAYS.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  76  90  77  91 /  20  40  20  40
STT  78  87  78  86 /  40  40  30  30

&&

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

$$

11/09


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