020
FXCA62 TJSJ 270800
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
400 AM AST Sat Apr 27 2024

.SYNOPSIS...

Unsettled weather conditions are expected to prevail today, with an
elevated risk of flooding, especially for the interior and
southwestern Puerto Rico. Some improvement is anticipated for the
first couple of days of the workweek, but the pattern will turn wet
again after Tuesday, with additional periods of showers and
thunderstorms. Marine and coastal conditions are expected to
deteriorate Monday onward as a northerly swell arrives.

&&

.SHORT TERM...Today through Monday...

Isolated to scattered showers affected the local waters of Puerto
Rico and the U.S. Virgin Islands overnight. Some of these showers
reached the eastern coast of Puerto Rico, leaving minor
accumulations over Humacao, Las Piedras and San Lorenzo. Similar
weather conditions are expected to persist through at least the mid-
morning hours. Low temperatures were observed in the mid to upper
60s across the mountains, and around the mid 70s along the coastal
and urban areas. Light winds from the east prevailed through most of
the night.

Another active day is anticipated as a plume of moisture moves into
the region, promoting moderate to locally heavy showers and isolated
thunderstorms. The latest model guidance are showing an increase in
moisture content by the mid-morning hours through the afternoon with
precipitable water values ranging from 1.90 to 2.20 inches. This
moisture content in combination with diurnal heating, local
orographic effects, and sea breeze may lead to deep convective
activity over Puerto Rico. Therefore, the rainfall risk is elevated
today for the eastern, central interior and southwestern portions of
Puerto Rico, including the San Juan metro area. Due to previous
rains, soils are very saturated and additional rains could lead to
flash flooding, river rises, and mudslides. We encourage residents
and visitors to stay aware and monitor the weather forecast in your
location to plan your weekend accordingly.

A strong surface high pressure located over the Carolinas in the
U.S. eastern coast will promote moderate northeast winds today.
Winds are expected to increase on Sunday, resulting in breezy
conditions during the first days of the week. Model guidances
continue to show an above-than-normal moisture through the rest of
the period, with a slight improvement on Monday. Prepare for a wet
and unstable weather pattern to persist for the next several days.

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

A high pressure system at the lower levels of the atmosphere will
drive the winds from the east at the surface, and from the northeast
a little bit aloft. This feature will maintain the moisture trapped
in the lower levels of the atmosphere. In general, Tuesday looks
like the driest day of the forecast period, but moisture will still
remain at seasonal levels, triggering convection in the interior and
southwestern Puerto Rico.

The pattern will turn wet again for the rest of the workweek as yet
another mid and upper level trough digs into the western Caribbean.
This trough will pull plenty of moisture from the Caribbean Sea into
the local islands, and precipitable water values will be above
normal. On Wednesday, the steering flow will be from the southeast,
so local effects should trigger for the interior, north and
northwest of Puerto Rico, as well as around the Virgin Islands and
local waters. Then, on Thursday, as the trough further approaches,
the steering winds will collapse, with very light winds anticipated.
Additionally, the mean flow will be from the southwest, so activity
could switch focus for the eastern interior, the San Juan metro
area, and then the Virgin Islands.

One thing that could delay the development of rain, however, is that
if a thick cloud layer get established, then local effects will be
milder. Also, temperatures could be below normal for a change,
except for the southern coast of Puerto Rico, where values are still
expected to reach the low 90s. On the other hand, if there are
breaks of sunshine, then the risk for showers and thunderstorms will
be elevated, likely producing urban and small stream flooding, water
surges along rivers, as well as mudslides.

By Friday, the influence of the mid and upper level trough
diminishes, but a surface reflection remains, maintaining enough
moisture, and a light wind flow from the northeast. More moisture
will also be added into the mixture from another trough approaching
the eastern Caribbean from the east.  Thus, another active afternoon
is anticipated for the interior of Puerto Rico, with activity then
spreading toward the coastal areas. Since some drier air will filter
at the mid and upper levels, temperatures will warm up again to more
seasonal values, reaching the mid and upper 80s, and even the low
90s.

On Saturday, the pressure gradient begins to recover as a surface
high pressure exits the eastern coast of the United States. The
winds will be around 10 knots, and out of the southeast. Lingering
moisture around the northeastern Caribbean will maintain a showery
pattern, with another active afternoon and an elevated risk for
flooding and mudslides.

&&

.AVIATION...
(06z TAFs)

Mainly VFR conds expected across all terminals through the forecast
period. However, areas of SHRA/TSRA could produce tempo
MVFR/IFRcondsandmtnobsc, mainly over TJPS/TJBQ aft 27/14z. VCSH
expected at TJSJ/TIST/TISX terminals after 27/13z. ENE winds btw 9
to 14 knots with by higher gusts and sea breeze variations aft
27/13z.

&&

.MARINE...

A small northwesterly swell will continue to spread across the
local waters today into the rest of the weekend. Winds will
prevail from the east and becoming northeast today under the
influence of a surface high pressure moving off the eastern coast
of the United States. A northerly swell is anticipated to spread
across the local waters early next week deteriorating coastal and
marine conditions. Therefore, building seas are forecast from
Sunday into Monday across the offshore Atlantic waters, with seas
up to 7 feet. Small craft operators are urge to stay tune for
further advisories.

Additionally, showers and thunderstorms will continue to affect
the local waters for the next several days as lingering moisture
from a surface trough/old frontal boundary remains over the local
area.

&&

.BEACH FORECAST...

Breaking waves around 5 feet will maintain the risk of rip currents
moderate through Sunday along the north facing beaches of the
islands. A northerly swell will be arriving on Monday, increasing
the risk for these beaches to high through at least late
Wednesday.

&&

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

$$

SHORT TERM & AVIATION...GRS
LONG TERM & BEACH FORECAST....ERG
MARINE ...LIS