Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 221502

Area Forecast Discussion
National Weather Service San Juan PR
1102 AM AST Tue Jan 22 2019

.UPDATE...Scattered showers were observed across the northeastern
and north central sections of PR during the morning hours. A cold
front north of Hispaniola is forecast to stall just north of the
area during the next day or so. East to northeast winds will
gradually increase through Thursday as a strong surface high
pressure behind the front moves from the western Atlantic into the
central Atlantic. This will cause breezy conditions and passing
showers across the islands during this period. The main hazard
will be the marine conditions, please refer to marine update


.AVIATION Update...Trade winds showers will continue to affect
the USVI/PR terminals at times through the forecast period. This
should cause mainly RA/VCSH across the area terminals. Tempo MVFR
conditions are possible. Latest 22/12z TJSJ upper air sounding
indicated ENE winds at 8-17 kt blo FL100.


.MARINE Update...Seas and winds will gradually increase across
the regional waters tonight. A northwest swell will move quickly
overnight and wind driven seas will follow through the end of the
week. Winds could range between 20-25 kt across the Atlantic
waters and hazardous seas up to 12 feet are expected by Wednesday
night. Overall, seas are expected to range between 6-12 feet
through the end of the workweek, with the higher seas across the
Atlantic waters and passages. Small craft advisories are in
effect, please refer to the latest marine weather message (MWWSJU)
for more information.

Also, life threatening rip currents are expected along the west,
north and east facing beaches of the islands through at least
Friday afternoon.


.PREV DISCUSSION... /issued 521 AM AST Tue Jan 22 2019/

SYNOPSIS...Frontal boundary across the western Atlantic is
expected to move south and east over the next few days but should
remain north of the local islands. Surface high pressure will move
east from the western Atlantic, causing an increase in the local
winds this afternoon and Wednesday. Upper level ridge will prevail
for the next several days.

SHORT TERM...Today through Thursday...

Although an approaching frontal boundary is expected to remain to
the northwest of the forecast area, it will promote a shifts in the
winds to the northeast today through Thursday. This wind flow is
expected to strengthen up to 25 mph late tonight into Wednesday as
the frontal boundary approaches the region. On Thursday, winds will
shift once again from the east as the associates surface high
pressure, now moving over the western Atlantic, continues to migrate
eastward. Embedded within this wind flow, patches of low-level
moisture will continue to bring cloud clusters and passing showers
to windward areas of the local islands, increasing in frequency as
the wind flow increases. This activity will be followed by showers
developing over portions of the interior and western Puerto Rico, as
well as downwind from the local islands and mountainous areas of
Puerto Rico each afternoon. Afternoon showers will favor the
southwestern quadrant of the island today and Wednesday, with a
shift to the northwestern quadrant on Thursday. However, due to the
presence of a mid to upper level high pressure meandering over the
region and an expected rapid motion of any developing shower,
significant rainfall accumulations are not expected.

LONG TERM...Friday through Wednesday...

The long term forecast does not look particularly active as drier
than normal air mass is expected with fragments of higher moisture
bringing brief showers. The winds are expected to be generally
from the east at around 10 to 15 mph, occasionally to 20 mph in
gusts across the coastal areas. Either a ridge or zonal flow is
expected in the upper levels in the long term, and the mid levels
should be fairly dry. All of this will promote a fairly stable
atmosphere for the most part, limiting the intensity and coverage
of the afternoon convection, while brief showers are expected
across eastern PR and the USVI in the early morning and overnight
hours. The only feature that could bring higher cloudiness and
somewhat persistent rain the expected fragmented front north of
the area that could bring higher moisture and cloudiness on

AVIATION...Mostly VFR conditions expected across all terminals. A
cloud cluster moving over TIST and TISX will result in BKN
conditions at FL050-070 and VCSH through 22/14Z. Afternoon showers
will result in VCSH at TSJU and TJMZ between 22/14 and 22/22Z.
Surface winds will be light and variable through 22/14Z, then
turning from the northeast and increasing up to 18 knots with higher
gusts. The strongest winds will affect TJBQ, TIST and TISX after

MARINE...Seas will gradually deteriorate today and will continue
hazardous for most of this week as a northerly swell invades the
local waters and the local winds increase. Small craft advisories
will go into effect starting late tonight or early Wednesday
morning. Moderate risk of rip currents today, but high risk of rip
currents expected starting this evening.


SJU  82  73  82  73 /  40  60  60  60
STT  84  73  83  73 /  20  20  40  40


PR...High Rip Current Risk from 6 PM AST this evening through Friday
     afternoon for North Central-Northeast-Northwest-San Juan
     and Vicinity-Southeast-Western Interior.

     High Rip Current Risk from Wednesday evening through Thursday
     afternoon for Vieques.

     High Rip Current Risk from Wednesday morning 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.

     High Rip Current Risk from Wednesday evening through Friday
     afternoon for St Croix.

AM...Small Craft Advisory from 2 PM Wednesday to 8 AM AST
 Saturday for Anegada Passage Southward to 17N-Caribbean Waters
 of Puerto Rico from 10 NM to 17N.

     Small Craft Advisory from 2 PM Wednesday to 2 PM AST Friday for
     Coastal Waters of Northern USVI and Culebra out 10 NM.

     Small Craft Advisory from 8 AM Wednesday to 8 PM AST Friday for
     Coastal Waters of Northern Puerto Rico out 10 NM.

     Small Craft Advisory from 2 AM Wednesday to 8 AM AST Saturday
     for Atlantic Waters of Puerto Rico and USVI from 10 NM to

     Small Craft Advisory from 8 AM Wednesday to 2 PM AST Friday for
     Mona Passage Southward to 17N.

     Small Craft Advisory from 2 PM Wednesday to 8 AM AST Friday for
     Coastal Waters OF Northwestern Puerto Rico out 10 NM.



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