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000
FXCA62 TJSJ 180910
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
510 AM AST Thu Apr 18 2024

.SYNOPSIS...

Trofiness aloft will persist through next week; thus, afternoon
convection due to local effects may result in thunderstorms across
the interior and western sections. Any persistent moderate to
locally heavy rain over the already saturated soils may result in
river flooding or sudden mudslides along steep terrains this
afternoon. A surface high-pressure migrating from the western
Atlantic to the Central Atlantic from this weekend into next will
promote an advective pattern from Sunday onward.

&&

.SHORT TERM...Today through Saturday...

Showers developed over Puerto Rico and the USVI throughout the early
morning hours, with up to half an inch near Trujillo Alto and less
elsewhere. Winds lightened and became variable with speeds around 3
mph at 4am this morning. Heavy rainfall yesterday caused Rio Grande
de Manati and Rio Cibuco at Vega Baja to overflow their banks,
causing flooding on the roads they intersect. Due to this Flood
Warnings were issued until the morning.

As the mid to upper-level and associated surface trough continue to
pass through region unstable conditions will persist. By this
morning, the surface trough has already moved past the USVI and due
to it`s positioning the surface winds will prevail from the NE today
with light to moderate speeds, with stronger gust during the
afternoon. By this afternoon the area will be under the stable side
of the upper-level trough, however diurnal heating, local effects
and lingering moist air will allow convection to bring heavy
rainfall mainly across the interior to western sections of Puerto
Rico. Due to previous days of heavy rainfall soils are already
saturated which will increase the chance of runoff resulting in
flash flooding and possible mudslides across areas with steep
elevation.

By tonight, conditions will begin to improve overall with the
exiting of the upper-level trough and the mixing of drier air into
the region as northerly winds prevail. A surface high begins to
build in the western Atlantic, causing wind speeds to increase from
the NE to N. Besides ongoing passing showers throughout the morning
for northern and eastern PR and the USVI, Friday afternoon still
holds a good chance to bring noticeable rainfall for southwestern
to interior sections of Puerto Rico. A similar pattern will
prevail on Saturday with southwestern Puerto Rico having the best
chance of heavier rain. Temperatures are expected to be slightly
cooler for northern coastal areas these days due to northerly
wind. Again, for these days, flooding of small streams and urban
areas remains totally possible with the heaviest activity mainly
across the interior to western sections of PR during the afternoon
hours.


.LONG TERM...Sunday through Thursday...

A surface high-pressure building north of the islands, promoting
an advective pattern, will bring occasional moisture surges across
the USVI and PR from Sunday onward. The winds will persist mainly
from the east to east-northeast, which may result in the areas
affected by passing showers being the islands` north and east
windward sections, especially during the night and morning hours.
These showers will bring periods of moderate to locally heavy
rains at times. The afternoon convection will be driven mainly by
local effects, diurnal heating, and sea breeze variations across
the interior and western sections daily. Additionally, the latest
model guidance suggests maximum temperatures near the normal
climatological values during the long term.

Around mid-week, an upper-level trough will approach from the
west, increasing the local instability, which, combined with the
sea breeze, orographic effects and diurnal heating could result in
the typical strong afternoon convection of a wet April.

&&

.AVIATION...
(06z)

VCSH are expected to continue across the local area through at least
tonight. Periods of reduced VIS and low CIGs are possible during the
afternoon with thunderstorm development. Winds are light and
variable this morning and then will become NE at 10-15 kts aft
18/14z, with stronger gusts.

&&

.MARINE...
A set of surface troughs, one to the northwest and other to the
northeast of the islands will promote light to locally moderate
northeast winds today. A small northeasterly swell will move across
the Atlantic water from today onward. The surface trough northeast
of the region and a surface high pressure building across the western
Atlantic will promote moderate to locally fresh trades by the
weekend.

&&

.BEACH FORECAST...
A northeasterly swell, spreading across the local Atlantic, and
the locally wind-seas will result in a moderate risk of rip
currents along the north and east facing beaches in PR and the
USVI. The northeasterly swell will continue throughout the
weekend.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&

$$

SHORT TERM...RC
LONG TERM....CAM