Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 301926
Area Forecast Discussion
National Weather Service San Juan PR
326 PM AST Thu Mar 30 2017
.SYNOPSIS...An old frontal system will return to Puerto Rico and
the U.S. Virgin Islands Saturday to increase the moisture and
showers activity in the area. The boundary will linger until late
next week. Late next week another boundary is set to approach the
area first to bring a short dry spell then to increase shower
activity ahead of it.
.SHORT TERM...Today through Saturday...Drier air behind an old
frontal boundary will hold through tonight and tomorrow allowing
only a few showers over the local higher terrain of the Cordillera
Central. The sounding revealed a cap strong enough to block even
parcels at maximum heating at 12 kft and current radar shows tops
no higher than this even though it also showed a few showers
moderately heavy for a few minutes at a time. On Friday
precipitable moisture reaches a minimum of just a little more than
one inch before the moisture associated with the old frontal
boundary that passed through earlier in the week returns from the
southeast. This boundary will then stall over the area and weaken
somewhat, allowing scattered showers to persist into next week. A
broad upper level ridge will cover the central Caribbean and
reinforce this mostly dry pattern. A weak ripple in the flow late
Saturday will enhance showers to a small degree.
.LONG TERM...Sunday through Friday...
Ridging at upper levels will persist for much of the week and
then the ridge will move through the area and to the east on
Friday. Several low level features will approach the area. On
Monday a weak front will dissipate just north of the area with
little effect. A second front will likewise weaken north of the
area on Thursday but will push the weakening frontal boundary and
its associated moisture over the area a little farther south and
allow some drier air in from the northeast. The approach of a
third front will enhance the convergence ahead of it mainly after
Friday (7 April) and end the drying trend that will have begun
Saturday, (the day after tomorrow).
.AVIATION...SHRA have formed over the Cordillera Central and some
mountain obscurations have occurred over the Luquillo range. But
the air has been to dry for further activity and SHRA are expected
to dissipate before 31/00Z. VFR conds will prevail at all TAF
sites in this drier air mass. Aft 31/16z SHRA will again form over
the hir terrain in PR but VFR should cont thru 31/22Z at all TAF
sites. Sfc winds from the NE at 10 kt with brief gusty winds
and sea breeze variations til 30/23z, then calm/light and VRB winds.
.MARINE...Seas at the outer buoy have risen to above 7.5 feet and
the wave watch model is now running about 2 feet too low there.
Current models show Atlantic seas peaking at around 6 feet on
Friday and the next significant swell trains will not be until
Sunday. Models persist at brining some 7 foot seas to the Atlantic
waters then. Caribbean seas will remain tranquil with winds and
seas remaining below criteria for small craft exercise caution.
.PRELIMINARY POINT TEMPS/POPS...
SJU 75 85 76 87 / 10 20 30 40
STT 73 85 75 84 / 10 20 10 30
PR...High Rip Current Risk through Friday afternoon for North Central-
Northeast-Northwest-San Juan and Vicinity-Southeast-Western
High Rip Current Risk from 6 PM AST this evening through Friday
afternoon for Culebra-Mayaguez and Vicinity.
VI...High Rip Current Risk from 6 PM AST this evening through Friday
afternoon for St.Thomas...St. John...and Adjacent Islands.