Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 212004
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
404 PM AST Sat Apr 21 2018

.SYNOPSIS...Strong surface high pressure across the central Atlantic
will continue to dominate the local area through the rest of the
weekend. Small patches of low level moisture will move across the
region from time to time until Sunday. An increase in low level
moisture is expected early next week. Upper level trough will
dominates the western Atlantic Monday through Wednesday next week.

&&

.SHORT TERM...Tonight through Monday...
Small patches of moisture embedded in the trades will continue to
move occasionally across the U.S. Virgin Islands, Vieques,
Culebra as well as across the eastern sections of Puerto Rico
overnight and early Sunday morning. This moisture will induce the
development of isolated to scattered showers across those sectors,
however, not widespread or significant precipitation is expected.
This moisture in combination with daytime heating and local
effects will continue to produce showers and thunderstorms over
western and interior sections of Puerto Rico Sunday afternoon.

The winds are expected to turn more from the east by Monday. This
wind flow will provide additional moisture across the local
islands. There is also an upper level trough that may be digging
just west of the local islands, increasing instability and also
increasing the chances for thunderstorms especially over several
sectors in Puerto Rico when the moisture, diurnal heating and
instability all combine on Monday afternoon. Isolated to scattered
showers can be expected for the USVI during the day with showers
possibly streaming off the islands.

.LONG TERM...Tuesday through Sunday...From previous discussion...
For Monday into Tuesday, a sharp increase in low level moisture
is forecast to occur, with best moisture and favorable upper level
atmospheric conditions expected on Tuesday. As a result, an
increase in showers and thunderstorms are expected by early next
week. By late in the forecast period, drier air mass is expected
to encompass the region from the east.

&&

.AVIATION...Prevailing VFR. Sct-Bkn cld lyrs nr FL025...FL050...
FL100. Isold Tops 150-180...except higher with Isold TSRA psbl ovr
PR til 21/22z where TEMPO MVFR conds psbl in and around
TJSJ/TJMZ/TJBQ. Isold SHRA ovr coastal waters and en route btw
islands durg prd. Sfc winds fm E around 15 kts with ocnly higher
gusts along coastal areas and with aftn convection.

&&

.MARINE...Seas diminished this afternoon and all marine areas are
now below 7 feet. However, small craft should exercise caution
across most areas due to seas up to 6 feet and winds up to 20
knots.

&&

.PRELIMINARY POINT TEMPS/POPS...
SJU  75  85  75  86 /  20  20  40  40
STT  75  87  75  86 /  20  20  40  40

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...High Rip Current Risk through Sunday afternoon for St Croix.

AM...None.
&&

$$

SHORT TERM...OM
LONG TERM....JF



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