606
FXCA62 TJSJ 190720
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
320 AM AST Tue May 19 2026

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

.KEY MESSAGES...
Issued at 320 AM AST Tue May 19 2026

* Breezy, to locally windy, east to east-southeast winds will steer
  periods of fast moving showers towards windward sectors and can
  cause unsecured items to blow around.

* An upper-level trough northwest of the islands, diurnal heating,
  sea breeze convergence, and local effects, will support the
  development of showers and isolated t-storms, particularly during
  the afternoon hours across western Puerto Rico (limited to
  elevated flooding risk). Lines of showers can also develop
  downwind of the local islands and El Yunque.

* Breezy conditions will also continue to sustain choppy seas and
  hazardous marine conditions. A Small Craft Advisory remains in
  effect for the offshore Atlantic through at least Wednesday
  afternoon.

* A limited heat risk will persist this week, with heat indices
  ranging from the mid-90s to the low 100s across urban and coastal
  areas each afternoon.

* Up to a moderate risk of rip currents will continue this week,
  mainly along the north, east, and south-facing beaches of Puerto
  Rico, Vieques, Culebra, and the U.S. Virgin Islands.

&&

.Short Term(Today through Thursday)...
Issued at 320 AM AST Tue May 19 2026

Current satellite derived precipitable water (PWAT) values indicate
below normal to normal columnar moisture over the area. PWAT values
are currently at around 1.35 inches over the USVI, at 1.40 inches
over Vieques, Culebra, and eastern PR, and around 1.13 inches over
central to western PR. Even with these below normal values, shallow
moisture and breezy east to east-southeast winds have in part lead
to the development of fast moving showers. These have continued to
be steered towards the eastern region during the overnight hours. At
least minimal accumulations have been detected since midnight over
the eastern half of PR, south-central PR, Vieques, Culebra, and the
USVI. Patchy fog has also been detected over sectors of interior PR.
Lows have been in the low 70s to locally near 80 over urban and
coastal sectors of the islands, and in the upper 50s to the 60s at
higher elevations of PR.

A strong surface high over the Atlantic will continue to promote
breezy, to locally windy, east to east-southeast winds through the
rest of the period as it tightens the local pressure gradient. This
flow will continue to steer moisture over the islands, with PWAT
values climbing back to normal values today and tomorrow (1.50 to
1.90 inches). Current model guidance suggests that a patch of drier
air (with below normal PWAT) can reach the islands once again by
Thursday but uncertainty remains. PWAT values can locally reach
above normal values (above 2 inches) during afternoon convection,
each day. An amplifying mid- to upper- level trough NW of the
islands during the period can add some instability and increase the
frequency of showers. However, the presence of patches of drier air
in the mid- levels can help inhibit this activity. The breezy, to
locally windy, east to east-southeast steering flow will continue to
result in quick moving showers advecting towards windward sectors of
the islands during the next few days. This can resulting in periods
of variable to showery weather and in ponding of water over roads
and poorly drained areas, with a chance of urban and small stream
flooding. Diurnal heating, local orographic effects and sea breeze
convergence will also result in afternoon convection each day. These
convective showers and t-storms will develop over interior towards
the western half of Puerto Rico. This will result in a limited to
elevated flooding risk and flood advisories might need to be issued
each afternoon. Lines of showers can also develop downwind of El
Yunque, and the USVI towards eastern PR. Galvez-Davidson Indices are
forecast at up to around 25 to 30 today and tomorrow. A similar
pattern is forecast tomorrow, and, depending on if the patch of
drier air reaches the islands, a somewhat inhibited pattern on
Thursday. The breezy, to locally windy, flow can also limit rainfall
accumulations as showers and t-storms move faster. However, this
flow can result in unsecured items blowing around. Current model
guidance suggests that 925 mb wind speeds will continue at above
normal values for this time of the year. 925 mb temperatures
however, will remain seasonal today and tomorrow, possibly reaching
above normal values on Thursday. This will result in warm to hot
conditions. Highs will reach the upper 80s to lower 90s across urban
and coastal areas, while heat indices exceed 100 degrees F, during
the afternoon hours. This will result in a limited heat risk. Low
concentrations of saharan dust will also reach the region from time
to time.

&&

.Long Term(Friday through Tuesday)...
Issued at 320 AM AST Tue May 19 2026

A typical weather pattern is expected over the long-term
forecast, though conditions may become unstable by the end of the
period. A E- ESE wind flow should prevail as a surface high
pressure building over the Western Atlantic will linger for the
next several days, resulting in breezy conditions across the
islands. The latest model guidance suggest PWAT values remaining
typical for this time of the year (between 1.5 and 1.75 inches),
with patches of moisture arriving from time to time. Nevertheless,
moisture content is expected to increase early next week as the
upper-level trough extending into the tropics should migrate
eastward, approaching the local area. From the latest model
guidance solutions, the trough may become a cut-off low, and while
approaching the region, it should gradually cool mid-level
temperatures, with strengthening upper- level winds (250 mb winds
up to 60 kt). These conditions should allow cloud growth and
ventilation, favorable for deep convection. The most likely
scenario is for windward sections to expect isolated to scattered
showers overnight into the morning hours, with the highest
potential for isolated thunderstorms on Monday. The combination of
diurnal heating, local effects, and sea breeze convergence,
afternoon showers and thunderstorms are very likely each day,
particularly over the interior and half west of Puerto Rico.
Additionally, island streamers may move over eastern portions of
Puerto Rico, including the San Juan Metropolitan Area. Although no
significant flooding or lightning threat is expected, ponding of
water over roadways and poorly drained areas is very likely, along
with minor flooding. In addition to rainfall, hazards that can be
expected in this scenario include gusty winds and lightning.

Warmer temperatures for this time of the year are likely, with heat
indices exceeding 100 degrees Fahrenheit, particularly over urban
and coastal areas of Puerto Rico and the U.S. Virgin Islands.
Although the heat threat should remain limited, this level may
affect individuals sensitive to heat even more without adequate
hydration and long sun exposure.

&&

.AVIATION...
(06Z TAFS)
Issued at 320 AM AST Tue May 19 2026

Mainly VFR conditions across the terminals. E to ESE winds will
steer rounds of -SHRA/VCSH towards windward terminals during the
period. Btwn 19/16-23Z, SHRA/+SHRA, with isolated TS, will develop
across interior to W PR. This can result in brief MVFR conditions
over TJBQ. Lines of -SHRA/SHRA can also develop from the local
islands and El Yunque, affecting TJSJ. Breezy, to locally windy E to
ESE winds up to 15-20 kts after 19/13Z, with higher gusts and sea
breeze variations, decreasing after 19/23Z.


&&

.MARINE...
Issued at 320 AM AST Tue May 19 2026

A strong surface high pressure over the western Atlantic will
promote moderate to fresh trades through midweek. Winds will turn
more east to southeast thereafter as the surface high moves into
the central Atlantic. These breezy conditions will maintain choppy
seas, particularly across the offshore and exposed Atlantic and
Caribbean waters. A Small Craft Advisory is in effect for the
offshore Atlantic waters through at least late tomorrow. Afternoon
and early evening isolated thunderstorms can be expected each day
across the western waters of Puerto Rico.

&&

.BEACH FORECAST...
Issued at 320 AM AST Tue May 19 2026

A moderate risk of life-threatening rip currents will prevail across
the east, north, and south-facing beaches of Puerto Rico, Culebra,
Vieques, and the U.S. Virgin Islands throughout the workweek due to
persistent breezy easterly winds and choppy seas. A moderate risk of
rip currents means that life-threatening rip currents are possible
in the surf zone, and beachgoers should exercise caution when
entering these beaches.

If you become caught in a rip current, yell for help. Remain calm,
do not exhaust yourself and stay afloat while waiting for help. If
you have to swim out of a rip current, swim parallel to shore and
back toward the beach when possible. Do not attempt to swim directly
against a rip current as you will tire quickly.

For additional information and location-specific rip current
details, visit weather.gov/beach/sju.

&&

.FIRE WEATHER...
Issued at 320 AM AST Tue May 19 2026

A gradual increase in moisture today could prevent RH values from
decreasing below threshold values for prolonged periods; however,
rainfall should remain limited across the southern plains, allowing
relative humidity to drop to critical fire weather thresholds in the
region. Additionally, sustained winds of 15 to 20 mph, with higher
gusts, combined with elevated KBDI values, will favor the rapid
spread of wildfires across the southern coastal plains. The low 7-
day percent of normal rainfall will also persist across the
southeastern coastal plains. Fire management partners are urged to
remain vigilant.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...None.
VI...None.
AM...Small Craft Advisory until 6 PM AST Wednesday for AMZ711.

&&

$$

SHORT TERM/AVIATION/FIRE WEATHER/KEY MESSAGES...MRR
LONG TERM....MNG
MARINE/BEACH FORECAST...DSR

NWS SJU Office Area Forecast Discussion