Area Forecast Discussion
Issued by NWS San Juan, PR

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233
FXCA62 TJSJ 201500
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1100 AM AST Tue Feb 20 2018

.UPDATE...Forecast on track, breezy to windy conditions to
continue across the area. A generally fair and stable weather
pattern will continue to prevail with some passing showers
possible across east Puerto Rico as well Vieques, Culebra, and
the USVI. Moisture advection is expected on Wednesday to increase
the chance of shower activity across the area.

&&

.AVIATION...VFR conds are expected to prevail through the
forecast cycle with brief -SHRA/SHRA still possible at the
Leeward and USVI terminals as well as JSJ/JBQ. ENE winds
15-20 knots with higher gusts, becoming at around 10-12
knots overnight.

&&

.MARINE...Surface high pressure north of the region will produce
hazardous seas across the local waters and all passages much of
this week due to fresh to strong east northeast trade winds it is
generating. Expect seas 8 to 10 feet with occasional seas up to
11 feet across the offshore waters today building to 12 feet by
midweek.

&&

.PREV DISCUSSION... /issued 517 AM AST Tue Feb 20 2018/

SYNOPSIS...High pressure in the western Atlantic will move
southwest while weakening during the week. This will produce fresh
to strong winds that will slowly decrease after mid week. Areas of
moisture will move through bringing episodes of showers to the
smaller islands and windward sides of Puerto Rico. Little change
is expected in the weather pattern for the next 5 to 7 days.

SHORT TERM...Today through Thursday...
Strong surface high pressure over the W Atlantic will continue to
sink into the SW North Atlantic. Fresh to locally strong east to
northeast trade winds will prevail across the region as the
pressure gradient tightens. Trade wind showers will continue to
move at times from the Atlantic waters into the region, affecting
mainly the northern USVI and the northern and eastern sections of
PR. On Wednesday, the remnants of an old front and windy
conditions will increase the frequency of showers across the
islands. Drier air will fill in briefly on Thursday morning but
shower activity will increase once again during the evening hours
as an upper level short wave trof moves just to the east-
northeast of the region.

A wind advisory was issued for the USVI and Vieques due to expected
sustained winds around 25 mph. Breezy conditions are expected across
the rest of the region with gusts in the low to mid 30 mph. As winds
are forecast to gradually increase and peak on Wednesday another
wind advisory will be required for at least the northern and eastern
municipalities of PR.

LONG TERM...Friday through Wednesday...
Fading high pressure in the western Atlantic will continue to
drive moderate to fresh east northeast trade winds across the
area. Patches of moisture will form in the low level flow and
become progressively wetter with strong fluctuations in moisture
through the period generating increasing showers that will remain
brief and shallow but become more frequent and affect more of the
island of Puerto Rico during the period. An upper level jet
around a high building over the western tropical Atlantic will
grow over the area and translate to the northwest maintaining
subsidence at mid and upper levels through the period. Friday
should be the coolest day of the period with the GFS 1000-850 mb
thicknesses increasing afterward. Otherwise little change in the
overall pattern will be noted.

AVIATION...Mainly VFR conditions are expected to prevail through
forecast period. However, SHRA will continue to move at times early
this morning across TJSJ/TIST creating possible MVFR cigs. SHRA
expected to increase once again after 21/00z across the northern PR
terminals and TIST. East-northeast winds will prevail at 15-25 knots
with higher gusts after 20/14z. Sea breeze variations are possible
across the southwestern quadrant of PR. Winds back from NE to NW
and increase from 25 to 40 knots btwn FL170-350.

MARINE...Winds will be raising seas and short period swell during
the next 48 hours. Only sheltered areas on the western side of
Puerto Rico will escape small craft advisories and small craft
should still exercise caution there for winds. Winds will slowly
subside later in the week, but seas are expected to remain
hazardous in all but the waters least exposed to northeast swell and
seas through the weekend.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  81  75  82  73 /  60  60  60  60
STT  85  73  84  72 /  60  60  60  60

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through late tonight for Central Interior-
     Culebra-Mayaguez and Vicinity-North Central-Northeast-
     Northwest-San Juan and Vicinity-Southeast-Vieques-Western
     Interior.

     Small Craft Advisory from 8 AM Wednesday to 8 PM AST Friday for
     Southeast.

     Wind Advisory until 6 PM AST this evening for Vieques.

VI...High Rip Current Risk through late tonight for St Croix.

     Wind Advisory until 6 PM AST this evening for St Croix-
     St.Thomas...St. John...and Adjacent Islands.

     Small Craft Advisory until 6 PM AST Saturday for St.Thomas...St.
     John...and Adjacent Islands.

AM...High Rip Current Risk through late tonight for Coastal Waters of
     Southern Puerto Rico out 10 NM.

     Wind Advisory until 6 PM AST this evening for Coastal Waters of
     Northern USVI and Culebra out 10 NM-Coastal Waters of
     Southern USVI Vieques and Eastern Puerto Rico out 10 NM.

     Small Craft Advisory until 8 PM AST Friday for Coastal Waters of
     Southern Puerto Rico out 10 NM.

     Small Craft Advisory until 6 PM AST Saturday 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 Northwestern Puerto Rico out 10
     NM-Coastal Waters of Northern Puerto Rico out 10 NM-Coastal
     Waters of Northern USVI and Culebra out 10 NM-Coastal
     Waters of Southern USVI Vieques and Eastern Puerto Rico out
     10 NM-Mona Passage Southward to 17N.

&&

$$

UPDATE...OM
AVIATION....OM



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