325
FXCA62 TJSJ 011454
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
1054 AM AST Wed May 1 2024

.UPDATE...

A variable weather pattern prevailed during the morning hours
across the local region. The heaviest activity was observed over
the southeastern sections of Puerto Rico. Due to the local effects
and the available moisture, a wet pattern is forecast for the
rest of the afternoon hours. Therefore, residents over the
northwestern and San Juan Metro areas could expect moderate to
heavy showers.

From Friday into the rest of the weekend, a more wet and
unsettled pattern is expected due to the arrival of an upper-level
trough and plenty of moisture across the area. Therefore, A
hydrologic Outlook was issued due to the elevated risk of flooding
across most of the region. Given the saturated soils and the
expected conditions, urban flooding and small stream flooding.
Residents should stay tuned for further weather updates.

&&

.HYDROLOGY...

Deep moisture and instability provided from a upper level trough
will bring periods of showers and thunderstorms across the local
islands during the next several days, particularly on Friday and
into the upcoming weekend. Based on the latest guidance, the most
likely time period for the heaviest rainfall activity is Friday
afternoon into Saturday. As a result, there is an increasing risk
for ponding of water, flooding of urban areas, roads and small
streams. Life threatening flash flooding and mudslides are
possible as well. Given the some uncertainty, rainfall
accumulations will be available for the next day or so. A Flash
Flood Watch will likely be issued on Thursday.

.AVIATION...
(12Z)

SHRA/TSRA will continue to affect most of the TAF sites for the
rest of the afternoon. Ts in the mountains can result in ceilings
at FL030 across the interior PR and TJBQ. VCTS cannot be ruled
out at times during the fcst period but confidence not high enough
to add them at this moment for most terminals result in MVFR
conditions.

&&

.PREV DISCUSSION... /issued 516 AM AST Wed May 1 2024/

SYNOPSIS...

From today onwards, expect the instability and moisture levels to
increase once again, as a mid to upper level trough lingers over
the western Atlantic and moisture from the Caribbean is brought
into the area by east to southeast winds. Marine conditions will
remain hazardous through at least tomorrow. A High Risk of Rip
Currents will continue across western, northern, and eastern
coastline of Puerto Rico and Culebra.

SHORT TERM...Today through Friday...

Breezy conditions and scattered to locally numerous showers
prevailed once again during the overnight hours. Observed rainfall
amounts during the past 6 hours were from a quarter of an inch in
Patillas to 1.20 inches in Vega Baja and less than a quarter of an
inch across the U.S. Virgin Islands. Minimum temperatures were from
the mid-to-upper 70s across coastal areas to the mid-60s across the
higher elevations. Wind gusts were between 25-30 mph across the
northeast coast of PR and between 23-26 mph in St. Croix and St.
Thomas.

The forecast remains on track during the short-term period as a
wetter and unstable pattern will evolve as an upper-level trough
approaches the area from the west and an induced surface trough
develops north of the region. In response, moisture pooling and
lighter winds can be expected, further enhancing shower and
thunderstorm development across the local area. Due to already
saturated soils, any brief period of heavy showers or persistent
light rainfall could lead to urban and small stream flooding,
localized flash flooding, and mudslides, particularly across the
interior and the eastern half of Puerto Rico. Regardless, all the
islands could experience brief periods of heavy showers during the
next several days. Steering winds are still expected to shift
further from the S/SW on Thursday and Friday, increasing the
potential for showers across San Juan and its vicinity. Today, the
W/NW quadrant of PR should see more shower and thunderstorm
development during the afternoon than previous days as winds shift
more from the east to southeast. Please continue to monitor the
weather conditions and be alert for any possible issuance of flood
products.

High temperatures will remain in the mid-to-upper 80s along the
coastal and urban areas and from the mid-to-upper 70s along the
mountains and valleys. Minimum temperatures will range from the mid
and upper 70s across coastal areas to the mid-60s in the higher
elevations

LONG TERM...Saturday through Tuesday...

The long-term period continues to lean towards a wet and unstable
weather pattern across Puerto Rico and the U.S. Virgin Islands.
As mentioned in the previous discussion, this weather pattern
should prevail as a surface trough and a perturbation over the
northeastern Caribbean merge across the forecast area, allowing
rainfall activity to be the dominant feature throughout the long-
term period. On Saturday, the upper level, yet maxima, should
remain to the north of the area. Nonetheless, winds around 60
knots will still reach the region. At this time, models suggest
Saturday as the wettest and most unstable day of the period. The
Precipitable Water (PW) models show values above two standard
deviations by the early part of the weekend. The 500 mb
temperatures also suggest values around -8 degrees Celsius on
Saturday, meaning that there is potential for some isolated
thunderstorm activity across Puerto Rico and the U.S. Virgin
Islands. Despite the fact that Saturday looks like the most
unstable day, we can not rule out rainy days for the rest of the
period. The latest model guidance suggests enough moisture
extending across all levels of the atmosphere through Tuesday,
meaning that rainy days are ahead. This increase in moisture
content is due to a broad patch of moisture or perturbation over
the Caribbean that will be absorbed and brought into the area by a
strong trough. We anticipate active afternoons each day with the
potential increase in the frequency of showers and isolated
thunderstorms. Overall, the main hazards from Saturday into
Tuesday are the increased risk of flooding across the islands and
the risk of mudslides, particularly in areas of steep terrain in
Puerto Rico. Therefore, we encourage citizens and visitors to be
aware of any additional updates in the forecast.

AVIATION...
(06z) TAFS

SHRA/TSRA with max tops around FL300 were observed across the
Caribbean waters, and increasing across the Atlantic coastal waters
overnight. This activity should impact manly TJPS thru 01/13z with
possible tempo MVFR to IFR conds. Across, TJSJ/TIST/TISX/TJBQ mostly
VCSH and -SHRA at times expected with brief MVFR cigs. Mtn top obscd
and BKN/OVC lyrs will continue across PR. TSRA could develop later
this afternoon near TJBQ/TJSJ causing tempo MVFR to brief IFR conds.
East winds at 13-17 kt with stronger gusts near showers. VCTS cannot
be ruled out at times during the fcst period but confidence not high
enough to add them at this moment for most terminals.

MARINE...

A surface high pressure extending from the western to central
Atlantic will tighten the local pressure gradient, promoting moderate
to locally fresh trade winds across the Northeast Caribbean through
at least tomorrow. As a result, expect hazardous seas for small craft
operators due to confused seas associated with the increasing winds
and a northeasterly swell spreading across the local waters. An
induced surface trough, north of the islands, will weaken the
pressure gradient and winds will shift from the east to east-
southeast by the latter part of the week.

BEACH FORECAST...

A northerly swell and strong winds are resulting in High Risk of
Rip Currents across some of the local beaches. The High Risk for
western Puerto Rico, St. Thomas and St. John will continue
through Thursday morning, while for the northern, eastern PR, and
Culebra should remain through Thursday afternoon. For more
information and details about the latest forecast please refer to
the Surf Zone Forecast (SRFSJU) and the Coastal Hazard Message
product (CFWSJU).

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...High Rip Current Risk through Thursday afternoon for PRZ001-002-
     005-008-012.

     High Rip Current Risk through late tonight for PRZ010.

VI...High Rip Current Risk through late tonight for VIZ001.

AM...Small Craft Advisory until midnight AST tonight for AMZ711-712-
     716.

     Small Craft Advisory until 6 PM AST this evening for AMZ723-741-
     742.

&&

$$

SHORT TERM...LIS
PUBLIC...MRR