Area Forecast Discussion
Issued by NWS San Juan, PR

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FXCA62 TJSJ 230900

Area Forecast Discussion
National Weather Service San Juan PR
500 AM AST Mon May 23 2022

.SYNOPSIS...Relatively unstable conditions are forecast over the
next few days under the influence of an upper level trough/TUTT.
Surface high over the western Atlantic is supporting moderate
trade winds across the local islands. Max temperatures for the
week will be near normal, with highs in the upper 80s.


.SHORT TERM...Today through Wednesday...

Residents in Puerto Rico and the U.S. Virgin Islands can expect the
islands to move to a more unstable and wetter pattern than last
week. Expect more frequent passing showers moving across the
windward sections each day, followed by organized convection across
the interior and western areas.

Afternoon showers and thunderstorms will likely be more intense and
long-lasting due to a TUTT combined with a set of short wave
troughs, which are forecast to increase atmospheric instability,
especially today and Wednesday. Some instability parameters that
indicate favorable conditions for the formation of organized
convection are near to below-normal 250MB Heights, steep lapse rate
at low and mid-levels, below-normal temperatures at 500MB, the
disappearance of the trade wind cap, and MU CAPE ranging between
1500 and 2300, especially in the afternoon. Therefore, we are
anticipating the formation of thunderstorms, especially each
afternoon across the interior and western sections of Puerto Rico.
Also, we cannot rule out thunderstorm formation across the local
waters each night. This activity will produce periods of heavy
rainfall leading to urban and small stream flooding each afternoon.

.LONG TERM...Thursday through Tuesday...

An upper-level low/TUTT northeast of Puerto Rico and the U.S.
Virgin Islands will dominate the weather conditions. The proximity
of the TUTT will provide colder temperatures aloft, increasing the
instability late in the workweek. Although moisture will remain
near normal for this time of the year, high convective instability
associated with the TUTT will combine with the sea breeze convergence
to fuel afternoon showers and thunderstorms along the Cordillera
Central and western Puerto Rico. Aerosol models suggest some Saharan
Dust Thursday and Friday. This will limit the shower coverage but
the dust particles may enhance the thunderstorm activity as
concentrations are forecast to remain low. Another high pressure
builds over the western Atlantic late in the week into the
weekend, allowing the trade winds to veer from the east-southeast.
A drier and more stable pattern is possible during the weekend as
the upper-level trough moves away from the region. This will likely
result in mostly sunny conditions and warmer than normal temperatures
under a southeasterly flow from Saturday into early next week.


.AVIATION...VFR conditions will prevail through much of the forecast period.
However, at times, quick passing SHRA with moderate to heavy rain
periods could lower VIS at JSJ/IST/ISX. TSRA will also form across
the mountain areas of PR and near JBQ during the afternoon, where
mountain obscurations are also expected. Expect calm to
light/variable winds overnight, returning from the E-ENE at 10-15 kt
with higher gusts and sea breeze variations after 23/13z.


.MARINE...Moderate easterly winds of 10-15 kts and seas of 2-4
feet can be expected across the Atlantic and Caribbean waters most
of the week. Unstable conditions will increase the potential for
showers and thunderstorms across the regional waters. Moderate
risk of rip currents will continue for most of the beaches in
Puerto Rico and the U.S. Virgin Islands.


SJU  89  76  88  76 /  50  50  50  50
STT  86  76  87  76 /  30  40  40  50




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