National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXCA62 TJSJ 230821
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
421 AM AST Tue Apr 23 2024

.SYNOPSIS...
-- Changed Discussion --
A surface trough continue to impact the local islands, bringing
periods of showers and thunderstorms. Slight concentrations of
Saharan dust are expected today as well, so skies could be hazy.
The wet weather pattern will persist through the end of the
workweek, but drier conditions are anticipated late in the weekend
and early next week.
-- End Changed Discussion --

&&

.SHORT TERM...
-- Changed Discussion --
Today through Thursday...

The axis of the surface trough was located just west of Puerto Rico
during the early night hours. However, the most active part of the
trough was situated over the USVI, Vieques, and Culebra. Heavy
showers and strong thunderstorms pulsed throughout the night across
this region, with some reaching eastern portions of Puerto Rico.
Despite this area of activity, the night was much calmer than the
previous night. The greatest rainfall accumulations estimated by the
radar were over western and eastern St. John and Puerto Rico,
respectively, with slightly above 1 inch each. Satellite and radar
data indicate an elongated convergence zone promoting heavy showers
persisting west of St. Croix. As this active area is advected
westward, expect cloudy skies and showery weather across the eastern
third of Puerto Rico during the morning hours, with some localized
areas possibly experiencing heavy showers.

According to TAFB surface analysis, the axis of the surface trough
is expected to persist over and near the CWA through at least the
end of the week. This is attributed to the deepening and approach of
a mid-level short-wave trough and surface frontal boundary from the
west, which will combine with the surface trough that has been
impacting us over the last day or so. This weather pattern will
maintain unsettled conditions for the rest of the short-term
forecast. The 1000-500mb thickness will gradually decrease
throughout the week, with steep 850-700 mb lapse rates.
Additionally, this setup will promote enhanced moisture convergence
across the region. Model guidance suggests precipitable water
content will remain within the range of 1.9 to above 2.0 inches for
most of the period, with slightly lower amounts across the eastern
half of the CWA by Thursday afternoon onwards.

USGS river sensors still indicate that most rivers over the eastern
half of Puerto Rico are exceeding the 75th percentile, with half of
them surpassing the 90th percentile or well above normal. Soil
saturation is also high, increasing the potential for excess runoff
and landslides in steep terrain. Therefore, the flood risk over the
eastern half of Puerto Rico will remain elevated for the rest of the
short-term forecast, as any additional rainfall could exacerbate
these factors. For the rest of the area, a limited to elevated
flooding risk will persist. Suspended Saharan dust particulates will
be present, promoting hazy skies in areas with limited shower
activity.

.LONG TERM...Friday through Tuesday...

As a shortwave trough digs into the western Caribbean, high clouds
are expected to get established over Puerto Rico and over the Virgin
Islands. At the surge, a high pressure over the central Atlantic
drives the trade winds from the east at speeds below 15 knots.
Moisture from a surface trough/old frontal boundary will linger into
the region, maintaining that pattern of showers reaching the region
at times. The moisture will finally be pushed south of the islands
late on Friday and early Saturday, as a high pressure exits the
eastern coast of the United States. This feature will push a drier
air mass into the islands, with precipitable water values falling to
near normal values on Saturday, and below normal all the way into
Tuesday. Winds will be from the northeast all this period, with a
more northerly component at times. It will be brisk too, with speeds
at 15 to 20 mph, and stronger gusts. In reality, is not going to be
completely dry, since some showers will still develop over the
Atlantic, reaching the USVI and northeastern PR at times, and some
showers will still develop in the afternoon over southwestern Puerto
Rico. However, they will not be as widespread or strong as the one
being experienced lately.
-- End Changed Discussion --


&&

.AVIATION...
-- Changed Discussion --
(06Z TAFs)

Mainly VFR conditions will prevail during the morning. SHRA ovr the
waters could promote MVFR conds thru 23/14z across USVI terminals.
Afternoon TSRA/SHRA could result in brief MVFR/IFR conditions,
mainly across PR terminals btwn 23/17-23z. After that, SHRA may
affect USVI terminals and TJSJ. HZ due to Saharan dust, but VSBY
should remain P6SM. Surface winds will remain from the east-
southeast at 5 to 10 kt but will then range between 10- 15 knots
with higher gusts after 23/13z.
-- End Changed Discussion --

&&

.MARINE...
-- Changed Discussion --
A surface trough crossing the islands will yield winds from the
southeast today. Showers and thunderstorms will continue to affect
the local waters today. A small northwesterly swell will arrive late
Wednesday and Thursday. Another surface trough will shift the winds
from the east by Wednesday, before switching from the northeast on
Saturday under the influence of a surface high pressure over the
western Atlantic.
-- End Changed Discussion --


&&

.BEACH FORECAST...
-- Changed Discussion --
Breaking waves of around 3 feet will maintain the risk of rip
currents generally low. The risk will become moderate again on
Wednesday night.
-- End Changed Discussion --

&&

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

$$

SHORT TERM...CVB
LONG TERM....ERG