Area Forecast Discussion
Issued by NWS San Juan, PR

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949
FXCA62 TJSJ 181545
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1145 AM AST Sun Feb 18 2018

.UPDATE...
The Terminal Doppler detected a few passing showers across the
northern U.S. Virgin Islands, the north and east portions of
Puerto Rico during the morning hours. Shower activity is expected
to decrease during the afternoon hours as a dry air mass moves
over the islands. However, satellite imagery showed patches of
clouds which could result in one or two brief passing showers.
Also, a few induce afternoon showers are expected across the
western municipalities of Puerto Rico. But in general, a
combination of sunshine and clouds will prevail across the
islands.

&&

.AVIATION...
VFR conds durg entire prd at all terminals. SFC WNDS fm the E at
15-22 kts with higher gusts will prevail through the evening.
Winds are forecast to drop around 10 kts overnight. No sig wx
impacts at terminals or ovr local flying area.

&&

.MARINE...
Winds and seas are forecast to increase late tonight and small
craft advisories are in effect from 8 pm AST this evening to at
least Monday evening. Mariners can expect increasing seas between
6 and 8 feet with occasional seas up to 10 feet and winds between
15 and 25 knots.

Beach goers should exercise caution due to a high risk of rip
currents across the north central and north western beaches of
Puerto Rico.


&&

.PREV DISCUSSION... /issued 352 AM AST Sun Feb 18 2018/

SYNOPSIS...Surface high pressure across the Atlantic to the
north of the local islands will produce moderate east to east
northeast winds across the local area today. The local pressure
gradient will tighten early in the workweek as a stronger surface
high pressure develops across the northwestern Atlantic.

SHORT TERM...Today through Tuesday...
Prevailing easterly trade winds will continue to increase today
through Tuesday, as the surface high pressure ridge will build
north of the region and tighten the local pressure gradient.

As a result, expect frequent passing low level clouds with
occasional showers to affect the forecast area, especially during
the evening and early morning hours. This will be followed by mostly
sunny skies and fair weather under breezy conditions each day. As
pressure gradient continues to tighten, expect windy conditions (20-
25 MPH) with stronger and more frequent gusts by Monday and Tuesday.

Apart from the cool advective pattern of shallow moisture and quick
passing trade wind showers, an overall dry and stable airmass will
dominate the region, as the mid to upper level ridge will remain in
place for the next several days. As previously mentioned, expect to
see an increase in the early morning shower activity along portions
of the north and east coastal sections of the islands, as the trade
winds increase. These showers will be of short duration with no
significant weather impacts at this time. The exception will be the
deterioration of the marine conditions which is forecast to begin
later tonight and continue through Tuesday. Surf Zone Conditions are
also forecast to deteriorate creating dangerous rip currents along
most of the local beaches. Stay tuned and remain alert to the local
weather and marine conditions.

LONG TERM...Wednesday through Monday...
An upper level trough is expected to amplify across the northeast
Caribbean Wednesday through Saturday. This feature will result in
an increase of moisture transport across the local islands and
surrounding waters. Strong surface high pressure is expected to
persist across the Atlantic waters, just to north of the local
islands until at least Friday. This surface high pressure will be
replaced by another strong high pressure Saturday through Monday.
Patches of moisture embedded in the east northeast trades will
continue to move over the forecast area at times, causing brief
showers over the local islands. These showers will affect mostly
the local waters, USVI, Vieques, Culebra as well as the northern
and eastern PR, especially during the nighttime and early morning
hours. The strong surface high pressure systems across the
Atlantic will cause the local pressure gradient to tighten early
in the workweek, which will cause windy conditions locally. These
winds will likely inhibit the usual sea breeze convergence in the
afternoon hours across western PR, which means that the areas that
could be affected by rain will probably be the USVI , Vieques,
Culebra and north and eastern PR, even during the daytime hours.
Wednesday through Saturday, looks to be the days with the best
moisture due to the presence of an upper level trough close to
the region. However, it is still expected to be somewhat windy so
the showers observe should be heavy but brief.

AVIATION...VFR conds durg entire prd at all terminals. SCT-BKN cld
lyrs nr FL025...FL050...FL080...SKC ABV. L/LVL WNDS fm ENE 15-20 kts
blo FL250. -SHRA/SHRA en route btw islands and ovr regional waters.
Few Tops btw FL100-FL120. Sfc wnds lgt/vrb bcmg 15-20 kts and gusty
aft 18/14z. No sig wx impacts at terminals or ovr local flying
area.

MARINE...Seas have diminished to around 6 feet across the local
waters, but will increase again tonight and Monday. Thus,
hazardous marine conditions are expected to continue through at
least mid week. As a result, small craft advisories will be in
effect. Winds up to 25 knots with higher gusts are expected.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  82  74  83  75 /  30  30  30  30
STT  84  72  85  73 /  30  20  30  30

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Small Craft Advisory from 8 PM this evening to 8 AM AST
     Wednesday for Southeast.

     High Rip Current Risk through late tonight for North Central-
     Northwest-Western Interior.

VI...Small Craft Advisory from 8 PM this evening to 8 AM AST
     Wednesday for St.Thomas...St. John...and Adjacent Islands.

AM...Small Craft Advisory from 8 PM this evening to 8 AM AST
     Wednesday 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 Puerto Rico out 10 NM-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.

     Small Craft Advisory from 8 PM this evening to 8 PM AST Monday
     for Coastal Waters OF Northwestern Puerto Rico out 10 NM.

&&

$$

SHORT TERM...CAM
LONG TERM....99
AVIATION...



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