Area Forecast Discussion
Issued by NWS San Juan, PR
FXCA62 TJSJ 110049
Area Forecast Discussion
National Weather Service San Juan PR
849 PM AST Sat Dec 10 2016
.UPDATE...Cloudiness and the shower activity over western PR
continued to move offshore and diminish during the late evening
hours. Isolated thunderstorms were also detected by the National
Weather Service doppler radar across the north sections of the
Mona passage during the late afternoon and early evening hours. By
late evening most of this activity had dissipated.
Skies will become partly cloudy to mostly clear over much of PR
during the overnight hours. However another surge of trade wind
moisture will move across the U.S. Virgin during the rest of the
evening and overnight. This low to mid level moisture with embedded
showers will reach the north and east sections of PR by early morning
bringing increasing cloudiness once again. Brief gusty winds may accompany
the passing showers as they reach the east coastal sections of the islands.
A gradual clearing is expected by late morning...followed by partly
cloudy to mostly sunny skies.
During the afternoon, available moisture convergence and diurnal effects
will lead to afternoon showers over parts of the interior and west
sections of PR, as well as in isolated areas of the San Juan Metro.
Due to the increasing trade winds, expect the developing showers
to quickly stream across the islands so expect no significant rainfall
accumulations is expected at this time. Only minor changes made to
the inherited short term Pops and Wx forecast based on present and
expected weather conditions. Updated the long term marine forecast
grids based on recent model guidance and Sea conditions.
.AVIATION UPDATE...Mostly VFR conditions expected across all
terminals through 11/24z. Will mention vcsh for TIST but will not
expect any impact on operations. Winds expected to remain at 6-10
kts overnight increasing to 12 to 15 knots with higher gusts from
the ENE after 11/13Z with sea breeze variations near TJPS, TJMZ
and TJBQ after 11/18Z.
.MARINE UPDATE...Seas will continue at up to 6 feet over the
offshore waters and local passages and winds between 15 to 20
knots with occasionally higher gusts. The increasing moderate to
fresh trade winds on Sunday and into early next week will create
rough and choppy Seas as previously mentioned. Small craft should
therefore exercise caution overnight through Sunday morning. Small
craft advisories will be in effect for portions of the coastal waters
early Sunday afternoon through at least Monday. Please refer to the
latest Coastal Waters Forecast issued by WFO San Juan PR.
.PREV DISCUSSION... /issued 202 PM AST Sat Dec 10 2016/
SYNOPSIS...Ridge pattern at mid to upper levels will dominate
the local region over the next several days. Conditions aloft will
remain fairly dry and stable...limiting the chances of thunderstorms
across the local area. At low levels...moisture embedded in the
trade winds will continue to reach the islands from time to time.
In general...trade wind pattern will prevail across Puerto Rico
and the U.S. Virgin Islands most of next week.
DISCUSSION...Only light passing showers were observed across the
local area this afternoon. Only some fast moving showers were
observed across the local islands. Afternoon showers across the
mountainous areas of PR are possible but the highest chance of
showers are expected to be across the western interior and western
sections of PR. Even then, the accumulations are expected to
produce generally minor ponding of water on roadways and poor
drainage areas. Some showers may stream off the USVI but no major
accumulations are expected over the islands.
High pressure across the Atlantic will continue to dominate the
local region next several days. Moisture embedded in the trade
winds will continue to reach the islands from time to time. In
general...trade wind pattern will prevail across Puerto Rico and
the U.S. Virgin Islands most of next week. Overall, no significant
weather events are forecast to affect the region in the long
AVIATION...VFR conds expected across the local terminals with a
prevailing easterly wind at about 10kt with sea breeze variations.
VCSH across TJPS and TJMZ after 10/18Z. Winds to decrease after
11/13Z becoming light and variable in most of the terminals.
MARINE...Seas up to 6 feet and winds up to 20 knots are expected
to prevail across the local waters through Sunday morning...increasing
up to 8 feet by Sunday afternoon. As a result...A small craft
advisory will be in effect from Sunday afternoon across most
.PRELIMINARY POINT TEMPS/POPS...
SJU 77 86 76 84 / 30 30 10 20
STT 77 87 75 86 / 40 20 10 30
PR...Small Craft Advisory from 2 PM Sunday to 8 PM AST Monday for
VI...Small Craft Advisory from 2 PM Sunday to 8 PM AST Monday for
St.Thomas...St. John.. and Adjacent Islands.
AM...Small Craft Advisory from 2 PM Sunday to 8 PM AST Monday for
Anegada Passage Southward to 17N-Atlantic Waters of Puerto
Rico and USVI from 10 NM to 19.5N-Caribbean Waters of
Puerto Rico from 10 NM to 17N-Coastal Waters of Northern
USVI and Culebra out 10 NM-Coastal Waters of Southern
Puerto Rico out 10 NM-Coastal Waters of Southern USVI
Vieques and Eastern Puerto Rico out 10 NM-Mona Passage
Southward to 17N.