NWS San Juan, PR wrote its last area forecast discussion before the first event at Apr 16, 3:00 AM AST, 10 hours 58 minutes earlier. Its key messages:
Area forecast discussion, Apr 16, 3:00 AM AST, 10 hours 58 minutes before
Area Forecast Discussion
National Weather Service San Juan PR
300 AM AST Thu Apr 16 2026
...New SHORT TERM, LONG TERM, AVIATION, MARINE, BEACH FORECAST...
.KEY MESSAGES...
Updated at 250 AM AST Thu Apr 16 2026
* A variable to unsettled weather conditions will continue
through Friday, promoting periods of showers and isolated
thunderstorms, particularly during the afternoon hours, with a
localized flooding risk.
* A moderate risk of rip currents will persist across several
beaches, especially along northern and eastern exposures, and
beachgoers should exercise caution.
* Conditions are expected to improve by Saturday as drier air
and more stable weather return, leading to a more typical
seasonal pattern with limited shower activity.
* Overnight showers will remain possible across the U.S. Virgin
Islands due to passing trade wind moisture.
&&
.Short Term(Today through Saturday)...
Issued at 250 AM AST Thu Apr 16 2026
A variable weather pattern prevailed during the night into the
early morning hours. Over the local waters, periods of showers
with strong thunderstorms affected the Caribbean and Atlantic
waters. Therefore, several marine weather statements and a Special
Marine Warning were issued during the night. Over land areas, some
showers developed across the southern coastal sections of Puerto
Rico, leaving between 1 and 1.5 inches of rainfall across
municipalities around Arroyo and Patillas. Around 2 AM, showers
diminished in that area and developed over the El Yunque region,
leaving around one inch of rainfall as well. Overnight
temperatures, as of 3 AM, were in the mid to upper 70s across
coastal areas and cooler across the mountains. Winds remained
light and from the southeast.
Today, the cut-off low clearly visible in satellite imagery will remain
northeast of the forecast area, while a deepening upper-level
trough persists, keeping the region under its divergent side to
the southeast. This setup, combined with a weak mid-level ridge,
will support cooler temperatures at 500 mb and promote some
instability across the area. From 0 to 3 km, winds will remain
similar to those observed yesterday, with a southeasterly
component at the surface (1000–850 mb) and a more southerly flow
at 700 mb, steering shower activity once again toward the
northwestern and northern sections of Puerto Rico. Therefore,
although widespread rainfall is not expected across the entire
island, afternoon convection will support periods of locally
strong showers with isolated thunderstorms, and gusty winds,
which may lead to urban and low-lying flooding where the heaviest
activity occurs. Temperatures will slightly increase during the
day due to the wind pattern and periods of reduced cloud cover,
with heat indices reaching around 100°F, especially across north-
central sections.
On Friday, as the upper-level trough amplifies further across the western
Atlantic, the forecast area will remain under its divergent side
to the southeast, allowing similar conditions to persist with
cooler temperatures at 500 mb and sufficiently favorable relative
humidity values between 850–500 mb to support shower development.
Model guidance suggests an increase in precipitable water, with
values ranging between 1.75 and 2.0 inches (around the 75th
percentile). Additionally, the Gálvez-Davison Index (GDI)
indicates the potential for isolated to scattered showers,
especially during the afternoon hours, along with a slight chance
of isolated thunderstorms over the surrounding waters. At the
surface, conditions will gradually shift as winds become more
easterly, with the induced surface trough moving farther west away
from the CWA and a surface high pressure system over the central
Atlantic dominating the local flow. Given these conditions, Friday
is expected to remain on the typical seasonal pattern, with
relatively quiet morning hours followed by a more active afternoon
characterized by showers across the Cordillera Central and the
western interior. As a result, an elevated flooding risk will
persist in these areas, as rainfall accumulations could enhance
the potential for urban and low-lying flooding.
Conditions will improve by Saturday, with the driest and most
stable day of the period. At the surface, precipitable water
values will decrease from around the 75th percentile to near the
50th percentile, remaining within a more typical seasonal pattern.
Additionally, at upper levels, the influence of the trough will
shift farther east, resulting in more stable and warmer conditions
at 500 mb. These factors will support mostly limited shower
activity during the morning hours, followed by localized afternoon
showers across the western sections of the islands. For the San
Juan metro area, afternoon conditions indicate around a 40% chance
of rain, which should still be generally suitable for the
Hurricane Hunter visit at Fernando Luis Ribas Dominicci Airport
in San Juan from 9 AM to 3 PM AST.
&&
.Long Term(Sunday through Thursday)...
Issued at 250 AM AST Thu Apr 16 2026
The latest model guidance continues to suggest an influx of
relatively drier air as a surface high pressure system dominates the
central Atlantic and a mid-level ridge establishes west of the
region. During the first half of the period, precipitable water
(PWAT) values will drop to seasonal normals of 1.25 to 1.50 inches.
Under the influence of the surface high, light to moderate easterly
winds will prevail through mid-week, shifting from the southeast
late Wednesday as another building high pressure located over the
western Atlantic begins to migrate toward the central Atlantic.
Overall weather conditions are expected to remain seasonal. Passing
showers are likely over the windward portions of Puerto Rico and the
U.S. Virgin Islands, followed by afternoon convective activity
across the central mountain range and western Puerto Rico, driven by
daytime heating and local effects. Due to this anticipated activity,
showers and isolated thunderstorms will likely persist from the
early afternoon into the evening.
Because of previous rainfall, soil saturation, and elevated river
levels, the potential for flooding remains an active concern.
Additionally, temperatures at the 500 mb level are projected to drop
to -8°C, increasing instability aloft and enhancing the potential
for afternoon thunderstorms. Surface temperatures are expected to
trend within seasonal values throughout the forecast period.
&&
.AVIATION...
(06Z TAFS)
Issued at 250 AM AST Thu Apr 16 2026
VFR conditions will prevail across all TAF sites during the
period, with brief MVFR conditions possible at TJBQ from 16/18Z to
16/22Z. Winds will remain from the southeast at around 5 knots,
increasing after 16/15Z to near 15 knots across the area, with sea
breeze variations. Afternoon showers and isolated thunderstorms
will lower ceilings and reduce visibility, particularly across the
Cordillera Central and northern sections due to SHRA and TS
activity. Winds will decrease again after 17/00Z, becoming more
easterly at less that 10 knots.
&&
.MARINE...
Issued at 250 AM AST Thu Apr 16 2026
A surface high pressure system over the eastern to central Atlantic,
interacting with surface trough north of the region, will promote
east-southeast light to moderate winds. A subsiding northerly swell
will continue to spread across the Atlantic waters, maintaining seas
from 5 to 6 feet across exposed areas, small craft should exercise
caution. Showers and thunderstorms associated to the trough will
continue across the local waters, creating locally hazardous marine
conditions through the weekend. Model guidance suggests another
long- period northerly swell that may arrive and spread across
local waters and passages by next week, resulting in choppy to
rough seas and becoming hazardous for small craft.
&&
.BEACH FORECAST...
Issued at 250 AM AST Thu Apr 16 2026
No changes were introduced to the beach forecast. Beach
conditions have been improving as the northerly swell continues to
diminish across the local waters and passages. Nevertheless,
straitening winds will result in breaking waves between 4 and 5
feet across northern beaches of Puerto Rico, including Vieques and
Culebra, and the U.S. Virgin Islands. Hence, a moderate risk will
continue for the next several days across the aforementioned
areas. Although there's no high risk, beachgoers should exercise
caution, as life- threatening rip currents remain possible along
beaches under moderate risk. A low risk risk will remain
elsewhere. Another long- period northerly swell may arrive and
spread across local waters and passages by next week.
Besides rip currents, beachgoers should remain weather alert as
showers and isolated thunderstorms are expected each day in the
afternoons, particularly over western and northern beaches of Puerto
Rico, and hazards may include gusty winds and lightning. For more
specific area details, refer to weather.gov/beach/sju.
&&
.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...None.
&&
SHORT TERM...LIS
LONG TERM....GRS
AVIATION...LIS