National Weather Service Today's Weather Impact Levels

805
FXCA62 TJSJ 041827
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
227 PM AST Sun Jan 4 2026

...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...

.KEY MESSAGES...
Issued at 225 PM AST Sun Jan 4 2026

* The risk of flooding increases from Monday into Tuesday across
  Puerto Rico, particularly during the afternoon and evening
  hours, with a limited risk of lightning as a front and an upper-
  level trough influence the region.

* Across the US Virgin Islands,the potential for shower activity
  will increase from Monday through early Tuesday morning,
  followed by a drier trend for the remainder of the week.

* A moderate risk of life-threatening rip currents will persist
  the rest of today along north- and east- facing beaches. A high
  rip current risk is expected by the middle of the week as a
  longer- period northeasterly swell reaches the local waters,
  affecting beaches facing the same direction in PR and the USVI.


&&

.Short Term(This evening through Tuesday)...
Issued at 225 PM AST Sun Jan 4 2026

Calm weather conditions prevailed across the islands today. A few
occasional showers moved across the USVI and eastern PR. Clear
skies were observed early in the morning, with cloudiness
increasing late in the morning into the afternoon. Temperatures
ranged from the mid-80s in windward areas to the upper 80s in
leeward areas, while mountain areas recorded temperatures in the
upper 70s to low 80s. Winds were from the southeast at 5 to 15
mph.

A mid- to upper-level ridge will persist through Sunday, promoting
dry air and subsidence aloft, as indicated by the JSJ 04/12Z
sounding, which shows dry conditions above 650 mb. This pattern
will generally limit widespread deep convection. At the surface,
southeast winds driven by high pressure over the central Atlantic
will continue. By Monday afternoon into Tuesday, a mid- to upper-
level trough approaching from the western Atlantic will increase
instability across the region. Surface winds will shift from east-
southeast to southerly, then turn northerly as a cold front and
pre-frontal trough approach, promoting moisture pooling over
Puerto Rico and the US Virgin Islands.

Later this afternoon, local effects will drive showers mainly
across northwest Puerto Rico. The advection of passing showers
may continue overnight into early Monday across the USVI and the
windward locations in PR.

Regarding hazards, today may bring periods of moderate to locally
heavy rain across northwest and north-central Puerto Rico, with
ponding on roads and poorly drained areas. On Monday afternoon and
evening, an elevated risk of flooding rains is expected the
Cordillera Central, spreading into the coast of Puerto Rico, with
a limited risk of thunderstorms. The US Virgin Islands will have
a limited risk of excessive rainfall. A limited lightning risk
exists across Puerto Rico and the US Virgin Islands from Monday
afternoon into early Tuesday, decreasing on Tuesday. By Tuesday,
excessive rainfall risk should be limited and focused mainly over
interior and southeastern Puerto Rico.

The frontal boundary has a good chance of crossing the islands
during the early morning hours of Three Kings Day (Tuesday),
followed by a somewhat drier, cooler air mass in the afternoon.

&&

.Long Term(Wednesday through next Saturday)...
Issued at 247 AM AST Sun Jan 4 2026

Compared to the earlier part of the week, drier and more stable
conditions are expected to return during the long term period.
After the frontal passage, a downward trend in the precipitable
water content is expected, as PWAT values drop to near 1 inch by
Wednesday, well below seasonal values, and remain in the 50th
percentile for the rest of the period. This is due to a ridge
pattern building from the western Atlantic early in the period,
and a TUTT-low developing northeast of the region during the
weekend. The driest period is expected between Wednesday and
Thursday, with the latest GFS guidance suggesting low-to mid-level
RH values of 10-40%, which are within the 25th-50th percentile.
Therefore, a very dry layer is expected to suppress cloud/shower
development in general. Thereafter, moisture content slowly
recovers between 1.25-1.40 inches, mostly due to shallow patches
of moisture arriving with the trade winds, and favoring isolated
to briefly scattered showers across the windward areas of the
islands during the nighttime.

Minimum temperatures could reach the mid 50s across the higher
elevations of PR during the early morning hours of Wednesday and
once again on Thursday. Mostly due to the expected clear nights
and a northeasterly component in the winds. Across coastal areas,
lows are expected to range from the upper 60s to low 70s. Maximum
temperatures should range from the mid-70s across the higher
elevations to the mid-80s across coastal areas.

&&

.AVIATION...
(18Z TAFS)
Issued at 225 PM AST Sun Jan 4 2026

VFR conditions will prevail across all TAF sites during the
period. However, SHRA/+SHRA will form across the PR-NW quadrant
this afternoon. Most of the activity should remain in the VCTY of
local terminals and will dissipate by the evening. Improving
conditions overnight into early Monday morning. However, unsettled
weather will possibly impact the region from 05/15z onward due to
SHRA/TSRA. Winds will continue under sea breeze influence mainly
from the SE at 10-15 kt with higher gusts, becoming calm to light
and VRB during the overnight hours (23-13z) each day. Winds will
turn from the N-NE after 05/15z.

&&

.MARINE...
Issued at 225 PM AST Sun Jan 4 2026

A surface high pressure over the central Atlantic into the
northeast Caribbean, maintaining light to moderate east-southeast
winds across the regional waters through early Monday. A frontal
boundary with an associated polar trough approaching the local
waters will promote light northerly to northeasterly winds and an
increase in showers and thunderstorm activity late Monday into
Tuesday. Pulse of a longer-period northeasterly swell expected to
arrive by midweek will lead to deteriorating marine conditions,
particularly across the exposed Atlantic waters and the Caribbean
Passages. Small craft operators should continue to monitor
forecasts for potential changes in marine conditions.

&&

.BEACH FORECAST...
Issued at 225 PM AST Sun Jan 4 2026

A moderate risk of life-threatening rip currents is expected for
the rest of today along the north- and east-facing beaches of
Puerto Rico, including Culebra. The rip current risk is forecast
to decrease to low on Monday. The risk will increase again to
moderate on Tuesday, followed by a high rip current risk on
Wednesday and Thursday along north-facing beaches of Puerto Rico
and the US Virgin Islands, as a long period northeasterly swell
affects the Atlantic Coastline. A moderate rip current risk is
expected to persist along these exposed beaches for the remainder
of the week. Thus, beachgoers are urged to exercise caution, as
life-threatening rip currents remain possible, particularly along
exposed north- and east-facing beaches. Elsewhere across Puerto
Rico and the US Virgin Islands, the rip current risk is expected
to stay low through much of the week.

&&

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

$$

MORNING CREW...CAM/RVT
EVENING CREW...ICP/MMC

NWS SJU Office Area Forecast Discussion