Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 261430

Area Forecast Discussion
National Weather Service San Juan PR
1030 AM AST Thu Apr 26 2018

.UPDATE...Surface trough moving across the region has resulted in
scattered showers and isolated thunderstorms over the waters and
portions of the USVI and eastern PR. As the trough exits the
region later this evening, additional showers and thunderstorms
are expected to develop and affect the eastern interior, the
central and northwestern quadrant of PR during the afternoon
hours. Locally heavy rainfall will lead to urban and small stream
flooding. Also, mudslides are possible in areas of steep terrain.
Minor changes were made to the short term grids.


.AVIATION Update...No major change from previous forecast. Mtn
top obscd and MVFR cigs expected across PR as SHRA/TSRA develop
early this afternoon. Latest 26/12z TJSJ upper air sounding
indicated ESE winds at 4-15 kt blo FL080...westerlies abv and
increasing with height with 70 kt at FL400.


.MARINE Update...Seas continue in general between 3-5 feet and up
to 6 feet across the offshore waters. Winds from the ESE at 15-20
kt. Locally higher seas and winds possible with showers and
thunderstorms today.


.PREV DISCUSSION... /issued 440 AM AST Thu Apr 26 2018/

SYNOPSIS...Showers will continue to affect USVI and E PR early
this morning followed by locally induced afternoon showers and
thunderstorms across west and northwest Puerto Rico. A drier air
mass is expected to prevail Friday through early next week.

SHORT TERM...Today through Saturday...

Doppler radar indicated isolated to scattered showers across the
surrounding waters with a few of them affecting the northern U.S.
Virgin Islands, Vieques, Culebra as well as the eastern sections
of Puerto Rico from time to time overnight. However, not significant
precipitation was detected in association with this activity.
Latest satellites images as well as surface analysis depicted a
weak surface trough just across the Lesser Antilles overnight.
Moisture associated with this feature is expected to move over the
region this morning. As a result an increase in showers is
expected across the U.S. Virgin Islands and eastern sections of
Puerto Rico during the rest of the morning hours. The combination
of the surface trough with daytime heating and local effects will
induce the development of showers and possible thunderstorms
across interior and western Puerto Rico this afternoon. By Friday,
a strengthening upper and mid level ridge will build across the
area. Drier air and strong trade winds of 15 to 20 knots will
limit shower development across the area both days.

LONG TERM...Sunday thru Friday...

A mid to upper level ridge will hold across the forecast area
through at least Monday. This feature is expected to quickly erode
as a broad upper level trough establishes across the western
Atlantic and into the eastern Caribbean. The aforementioned trough
will promote moisture advection across the eastern Caribbean
Friday onwards.

If the forecast holds, expect seasonably conditions Sunday through
Thursday with locally induced afternoon showers and a few isolated
thunderstorms across the western interior and west areas of
Puerto Rico each day. The chance for showers and thunderstorms are
expected to increase by the end of the workweek under deep tropical
moisture and plenty of upper level dynamics associated with the
upper level trough.

AVIATION...SHRA are moving westward across the Leeward Islands,
USVI an eastern Puerto TAF sites this morning. Expect VCSH and brief
periods of SHRA across those taf sites until 26/14Z. SHRA will then
spread across other sectors of PR with mtn obscurations. MVFR will
occur after 26/16Z at TJBQ/TJMZ. Latest TJSJ sounding indicated a
variable wind flow from the surface to around 24K feet, becoming
northwesterly and stronger aloft.

MARINE...Seas are expected to range from 3 to 5 feet across all
waters except the offshore Atlantic waters where seas up to 6
feet are expected. East southeast winds 10 to 20 kts will prevail
over the next several days.


SJU  89  76  89  76 /  50  20  20  20
STT  86  76  86  76 /  70  20  20  20




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