861
FXCA62 TJSJ 012107
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
507 PM AST Wed May 1 2024

.SYNOPSIS...

Unstable conditions and increasing moisture levels will likely
persist during the rest of the workweek into the upcoming
weekend, as a mid to upper level trough lingers over the western
Atlantic and moisture from the Caribbean is steered by east to
southeast winds into the area. These conditions will maintain
excessive rainfall and lightning hazard risk at elevated levels.
Hazardous marine and life- threatening surf zone conditions will
continue through at least Thursday.


&&

.SHORT TERM...Tonight through Friday...

Variable to showery pattern prevailed across the islands today,
easterly winds veered to become more southeasterly with higher gusts
up to the low to mid 20s across several coastal areas. Areas with
higher accumulations of up to 1-3 inches focused across
northeastern and northwestern Puerto Rico, as well as the San Juan
metropolitan area. Wet and unstable weather conditions are
forecast through the short term period. This pattern will result
from an upper- level trough approaching from the west and an
induced surface trough developing north of the islands. Up to
above normal, above 2 inches, of Precipitable Water (PWAT) are
present across the islands. Up to above normal PWAT is expected
through the short term period. Steering winds will continue to
gradually veer and become more southeast, then becoming light and
more south to south- southwest Thursday and Friday. Highs were in
the mid to upper 80s across lower elevations of the islands (with
some sensors recording 90 degrees to the 70s across higher
elevations of Puerto Rico. Lows tonight will range from the mid to
upper 70s across lower elevations of the islands to the mid 60s
across higher elevations of Puerto Rico.

A Hydrologic Outlook (ESFSJU & ESFSPN) was issued this morning as
the above mentioned deep moisture and unstable conditions, along
with lighter winds, will promote shower and thunderstorm activity
across the region during the next several days, particularly on
Friday and into the long term period (the upcoming weekend). The
latest guidance suggests that the most likely time period for the
heaviest rainfall activity is Friday afternoon into the long term
period (Saturday). Soils are already saturated therefore only
brief periods of heavy showers or persistent light rain could
still promote urban and small stream flooding, localized life
threatening flash flooding, mudslides and river rises. The areas
forecasted to receive the highest rainfall accumulations are
south, southeast and east sections of Puerto Rico, as well as
Vieques, Culebra and the US Virgin Islands. Areas of the interior
and western half of Puerto Rico could experience brief periods of
heavy showers. Please stay tuned for future updates, including
flood related products. A Flash Flood Watch will likely be issued
tomorrow.

.LONG TERM...Saturday through Tuesday...

From previous discussion issued at 516 AM AST Wed May 1 2024

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...

(18Z TAFS)

VRB weather conditions will persist for the period. SHRA and TSRA
over the mountains may result in lower ceilings in the FL030 and
FL040. VCTS and SHRA are expected for TJBQ, TJSJ, & TJPS until
01/23Z. After that, winds will diminish until 02/14Z when pick again
from the E-SE at 15 knots or less with gusty winds near the showers.
Another round of showers is forecast for TIST & TISX from 02/06-
02/14Z, resulting in lower ceiling, SHRA and briefly MVFR
conditions.


&&

.MARINE...

A surface high pressure extending from the western to central
Atlantic will maintain the local pressure gradient tight through
tonight. As a result, expect hazardous seas for small craft operators
due to confused seas associated with winds and a fading northeasterly
swell spreading across the local waters, then improving conditions
from Thursday onwards. However, an induced surface trough will shift
winds from the east to east-southeast by the latter part of the week
while a wet and unstable weather pattern is anticipated.


&&

.BEACH FORECAST...

A northerly swell and strong winds will maintain a High Risk of
Rip Currents across some 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...LEE/ICP
AVIATION...LIS/ICP
PUBLIC...MRR/YZR