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611
FXCA62 TJSJ 170857
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
457 AM AST Sun May 17 2026

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

.KEY MESSAGES...
Issued at 455 AM AST Sun May 17 2026

* An upper-level trough will approach the islands today and increase
  the frequency of showers and isolated thunderstorms, prompting a
  limited to elevated flooding risk.

* These showers will be steered by E to ESE winds; afternoon
  showers and possible t-storms will also develop across interior
  to the western half of PR and downwind of El Yunque and the
  local islands.

* Above-normal temperatures will persist across the region to start
  the week, with heat indices reaching the upper 90s to low 100s
  during peak afternoon hours, especially across urban and coastal
  areas.

* Flooding concerns are forecast to again gradually increase and
  become more locally elevated late in this week and into the
  holiday weekend.

* A moderate risk of rip currents will persist this week mainly
  along north and east facing beaches of Puerto Rico (southern
  beaches at times), as well as beaches of Vieques, Culebra, and the
  USVI.

&&

.Short Term(Today through Tuesday)...
Issued at 455 AM AST Sun May 17 2026

Current satellite derived precipitable water (PWAT) values indicate
broad moisture over the islands steered by east to east-southeast
winds. PWAT values range from 1.57 to 1.65 inches, at normal values
for this time of the year. Showers continue to be steered towards
windward areas with at least minimal accumulations detected by
midnight over the eastern third of PR, interior PR, Vieques,
Culebra, and the USVI. Accumulations above 0.6 inches stayed over
the waters. Although t-storms did not develop over the local waters
overnight, they did develop just south and west of our local waters.
Patchy fog was also detected over sectors of interior PR. Minimum
temperatures have been in the mid 70s to around 80 over urban and
coastal sectors of the islands, and in the upper 50s to the 60s at
higher elevations of PR.

East to east-southeast winds will continue to steer broad moisture
towards the region today and Tuesday, with more intermittent patches
of drier air arriving on Monday. PWAT values will be generally at
normal values today and Tuesday, and reaching below normal values at
times on Monday. PWAT values can, however, locally reach above
normal values during afternoon convection. Moisture steered towards
the region today was also part of the moisture field of a tropical
wave that already moved south of the region over the Caribbean Sea.
An amplifying upper level trough will continue to approach the
region from the west today, moving over the area later today and
remaining during the period, this can promote increased instability
and increase the frequency of showers. The presence of patches of
drier air in the mid-levels can help inhibit this activity. Showers
will continue to be steered towards windward sectors, resulting in
periods of variable to showery weather. This can result in ponding
of water over roads and poorly drained areas with a chance of urban
and small stream flooding. The upper trough will also aid in the
development of afternoon convection, in addition to diurnal heating,
local orographic effects and sea breeze convergence. This afternoon
convection, showers and isolated t-storms, will develop over
interior towards the western half of Puerto Rico, as well as
downwind of El Yunque, and the USVI towards eastern PR. This will
result in a limited to elevated flooding risk and flood advisories
might need to be issued each afternoon. Galvez-Davidson Indices are
forecast at up to around 35 today, 30, tomorrow and 25 to 30 on
Tuesday. Although rain is expected, above normal temperatures will
continue today, as indicated by 925 mb temperature guidance. Highs
will reach the upper 80s to lower 90s across urban and coastal areas
while heat indices exceed 100 to 105 degrees F during the afternoon
hours. This will result in a limited to elevated heat risk. Current
guidance suggests more normal 925 mb temperatures tomorrow and
Tuesday, prompting a limited heat risk. Low concentrations of
saharan dust over the region will continue to sharply decrease today.

&&

.Long Term(Wednesday through Sunday)...
Issued at 455 AM AST Sun May 17 2026

A typical late spring to early summer weather pattern is expected
through the long-term period. Broad surface high pressure over the
northwestern Atlantic will maintain moderate to fresh east to east-
southeasterly winds across the local islands, with occasionally
strong winds at times. Winds are expected to strengthen further into
next weekend, supporting breezy to locally windy conditions.
At mid and upper levels, the area will remain between ridging to the
southeast and a lingering trough/low over the western Atlantic,
while weak disturbances move around the broader pattern and approach
the northeastern Caribbean. This pattern will help support periods
of increased instability and more favorable conditions for deeper
afternoon convection late in the week and into the holiday weekend.

Patchy moisture embedded within the trade winds will continue to
promote passing showers during the overnight and morning hours each
day, followed by afternoon showers and isolated thunderstorms mainly
across interior and western to northwestern areas. Although mid-
level conditions may remain somewhat marginal at times, the
combination of local effects and strong daytime heating should still
support deeper convection each afternoon. Flooding concerns are
expected to gradually increase and become more locally elevated late
in the week and into the holiday weekend, with locally heavy
rainfall, ponding of water on roads, and localized urban and small
stream flooding possible. Additional hazards will include lightning,
heat, and gusty winds, especially as outdoor activity increases
during the Memorial Day weekend.

&&

.AVIATION...
(06Z TAFS)
Issued at 455 AM AST Sun May 17 2026

Mainly VFR conditions continue. E to ESE winds will continue to
steer -SHRA/VCSH towards windward terminals from time to time. Btwn
17/16-23Z, SHRA/+SHRA, with isolated TS, will develop across
interior to W & NW PR. This can cause brief MVFR conditions over
TJBQ. At the same time, lines of SHRA can also develop from the
local islands and El Yunque, affecting TJSJ. E to ESE winds up to
around 16 kts, with higher gusts and sea breeze variations,
decreasing after 17/23Z.
&&

.MARINE...
Issued at 455 AM AST Sun May 17 2026

A broad surface high pressure over the central Atlantic will promote
moderate to locally fresh east to east-southeasterly winds across
the regional waters through at least today. From late today into
early next week, winds will turn more easterly as another surface
high pressure builds over the western Atlantic. These breezy
conditions will maintain somewhat choppy seas, particularly across
the offshore and exposed Atlantic and Caribbean waters. Seas are
expected to range between 4 and 6 feet during the next several days.
Afternoon and early evening isolated thunderstorms can be expected
each day across the northwestern waters of Puerto Rico.

&&

.BEACH FORECAST...
Issued at 455 AM AST Sun May 17 2026

A moderate risk of life-threatening rip currents will prevail across
the east, north, and southern beaches of Puerto Rico and the U.S.
Virgin Islands through next week. Beach goers should exercise
caution when entering these beaches. This means life-threatening rip
currents are possible in the surf zones, 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.

&&

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

$$

SHORT TERM/AVIATION/KEY MESSAGES...MRR
LONG TERM....ICP
MARINE/BEACH FORECAST...DS

NWS SJU Office Area Forecast Discussion