AFDSJU

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN JUAN PR
310 PM AST MON APR 18 2011

.SYNOPSIS...A DEEP LAYER TROUGH ACROSS THE CENTRAL ATLANTIC WILL
CONTINUE TO SEND CLOUDS AND SHOWERS TOWARD THE NORTHEAST CARIBBEAN
ISLES. A WETTER PATTERN IS EXPECTED BY MID WEEK AS ANOTHER MID/UPPER
TROUGH WILL BUILD NORTH OF THE LOCAL REGION.

&&

.DISCUSSION...SATELLITE AND RADAR IMAGERY SHOWED A BAND OF LOW LEVEL
CLOUDS WITH SOME EMBEDDED SHOWERS...SLOWLY DRIFTING SOUTHWARDS ACROSS
THE OFFSHORE ATLANTIC WATERS. ALTHOUGH...A GENERALLY DRY AND STABLE
AIR MASS REMAINS IN PLACE...ISOLATED CONVECTION WERE OBSERVED ACROSS
THE SOUTHERN SLOPES AND WESTERN SECTIONS OF THE PUERTO RICO...BUT
NO SIGNIFICANT RAINFALL AMOUNTS WERE MEASURED SO FAR THIS AFTERNOON.

AN INDUCED/INVERTED TROUGH LOCATED ABOUT 530 MILES NORTHEAST OF THE
FORECAST AREA THIS AFTERNOON...IS SUPPORTED BY A MID/UPPER LEVEL
TROUGH ALOFT. THE UPPER LOW IS EXPECTED TO WEAKEN TODAY AS QUICKLY
LIFT TO THE NORTHEAST. AT THE SAME TIME...SHORT WAVE VORTICES ACROSS
THE WESTERN ATLANTIC WILL HELP TO DEVELOP ANOTHER UPPER TROUGH NORTH
OF THE ISLANDS BY MID WEEK. GLOBAL MODELS ARE FORECASTING A STRONG
MID-LEVEL REFLECTION OF THIS UPPER TROUGH JUST NORTH OF THE ISLANDS.
AS THE MID/UPPER LEVEL TROUGH BECOMES BETTER DEFINED...IT WILL
QUICKLY ERODE THE SUBSIDENCE CAP ACROSS THE LOCAL ISLANDS. THE
EVOLVING PATTERN WILL FAVOR THE MOISTURE ADVECTION ACROSS
HISPANIOLA...PUERTO RICO AND VIRGIN ISLANDS THROUGH THURSDAY
AFTERNOON...WITH PWS TO PEAK AROUND 1.4 INCHES BY WEDNESDAY
EVENING/THURSDAY MORNING. OVERALL...WEATHER CONDITIONS WILL
BECOME GRADUALLY MORE CONDUCIVE TO RAINFALL BEGINNING MID WEEK AS
UPPER LEVEL DYNAMICS IMPROVE AND MOISTURE CONTENT INCREASE ACROSS
THE LOCAL AREA.

&&

.AVIATION...VFR CONDS EXPECTED AT ALL TAF SITES THROUGH THE
FORECAST PERIOD. BRIEF MVFR CIGS PSBL IN PASSING SHOWERS.

&&

.MARINE...A MODERATE SIZE SWELL WILL REACH THE ISLANDS TOMORROW
MORNING AND PEAK TUESDAY AFTERNOON. AFTERWARDS...SEAS WILL RANGE
BETWEEN 4 TO 6 FEET AT LEAST THROUGH THE END OF THE WEEK.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  73  84  73  84 /  30  20  30  30
STT  73  85  74  83 /  20  20  30  30

&&

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

$$