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FXCA62 TJSJ 091807
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
207 PM AST Tue Jun 9 2026

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

.KEY MESSAGES...
Issued at 208 PM AST Tue Jun 9 2026

* Dangerous heat will continue through much of the week. Heat
  indices may exceed 100F, especially across urban, coastal, and
  lower-elevation areas of Puerto Rico and the U.S. Virgin
  Islands. Heat Advisories may be needed at times.

* A wetter and more unstable weather pattern is expected on
  Wednesday and especially Thursday as a tropical wave interacts
  with an approaching upper-level trough, increasing the coverage
  of showers and thunderstorms across the region, and posing the
  greatest risk of flooding for Thursday.

* Traces of Saharan dust will persist through the forecast period,
  producing somewhat hazy skies and reduced air quality,
  especially trailing the wave into early Saturday.

* The potential for life-threatening rip currents will turn
  moderate from Thursday onward, first across St Croix, then
  spreading to the rest of the east and north-facing beaches in
  the USVI and PR.

&&

.Short Term(This evening through Thursday)...
Issued at 208 PM AST Tue Jun 9 2026

Warm and hot weather conditions prevailed today with heat indices
between 100 and 110 degrees Fahrenheit in many coastal and urban
locations in PR and the USVI. The Doppler radar observed little or
no rain this morning. At the time of writing, air temperatures
ranged from the upper 80s to the low 90s along PR and the USVI`s
coastal areas, to the mid- or low-80s in mountain areas. Winds
were mainly from the east at 10 to 15 mph, with higher gusts and
sea-breeze variations.

Heat indices remain dangerous for vulnerable communities this
afternoon; therefore, a Heat Advisory continues for coastal and
urban areas in Puerto Rico and the U.S. Virgin Islands. The
aforementioned excessive heating, combined with variations in sea
breezes and local factors, is expected to lead to showers this
afternoon, and we cannot rule out at least a thunderstorm in the
interior or western regions of Puerto Rico. However, the presence
of dry air and warmer-than-normal temperatures at 500 mb (in the
75th percentile for June) will limit this potential. Once again,
later this evening, the weather is expected to be calm, with
warmer-than-average overnight temperatures. Some showers may reach
the windward areas of Puerto Rico and the U.S. Virgin Islands.

For Wednesday, the subsidence ahead of the Thursday weak tropical
wave will promote a somewhat calm weather pattern, featuring
warmer-than-normal temperatures, dangerous heat indices, and a few
quick-moving showers across windward areas during the morning.
However, a polar trough amplifying across the western Caribbean
and later near the northeast Caribbean around Wednesday and
Thursday, will enhance instability and the potential for
thunderstorms. Therefore, although we are expecting calm weather
early on Wednesday, afternoon convection will develop across the
interior and western PR, as well as downwind from the USVI and El
Yunque into the San Juan metro. This pattern will increase the
risk of flooding and water ponding on roads and in poorly drained
areas, as well as isolated urban flooding.

Although the potential for warm and hot temperatures will persist
on Thursday, there is a greater chance of urban and small-stream
flooding, along with isolated flash flooding, as the tropical wave
interacts with the polar trough swinging across the region. Some
of the limiting factors associated with the aforementioned weather
pattern include possible cloud cover from the mid- to upper-level
trough, which could inhibit afternoon convection and reduce the
amount of heating we experience. That said, currently the most wet
and unstable weather potential for the short term is Thursday.
Therefore, we encourage our residents and visitors to monitor
weather conditions, as we will update them as conditions require.

&&

.Long Term(Friday through next Monday)...
Issued at 110 AM AST Tue Jun 9 2026

No major changes were made to the long-term forecast, as weather
conditions are expected to become drier and more stable over the
upcoming weekend and early next week. A surface high pressure
building over the Western Atlantic should increase the local
pressure gradient, leading to strengthening east-southeast winds and
resulting in breezy to locally windy conditions across the islands.
Friday has the highest potential for flooding and lightning, as
lingering moisture associated with a tropical wave and the proximity
of an upper-level trough should enhance afternoon convection. From
the latest model guidance, PWAT may vary between 1.7 and 1.9 inches,
which is typical for this time of the year, but shows abundant low
to mid-level moisture. Due to the proximity of the trough, mid-level
temperature should remain cooler than normal (500 mb temperatures
around -8 degrees Celsius), with enhanced vorticity, rising air, and
divergence aloft across the region, favorable for deep convection.
Additionally, the Galvez-Davison Index (GDI) suggests the potential
of isolated to scattered thunderstorms, particularly over the
western/northwestern side of the CWA in the afternoon. Although a
drier airmass will gradually filter into the region on Friday,
passing showers can still be expected during the morning hours over
windward sections of the islands, followed by afternoon convection
over interior and western/northwestern Puerto Rico. Additionally,
island streamers may develop and bring some showers into eastern
portions of Puerto Rico, including the San Juan Metropolitan area.
Rainfall accumulations could lead to ponding of water over roadways
and poorly drained areas, including minor flooding, over the
aforementioned areas. As the drier air mass continues to filter into
the region, patches of moisture may arrive throughout Saturday, with
shallow afternoon convection over western/northwestern Puerto Rico.
Sunday and Mondays forecast remains uncertain, as the latest global
model solutions show different outcomes for the CWA. The latest GFS
solution showed the upper-level trough lingering near the region,
with PWAT values remaining near above normal (up to 1.9 inches),
while the ECMWF solution suggests a mid-level ridge near the CWA,
with drier air in the 850 - 500 mb layer. Due to inconsistency with
the GFS solutions, Sunday and Mondays forecast was based on a
similar pattern to Saturday, with limited rainfall activity.

In terms of heat, warmer conditions may persist throughout the
forecast period as model guidance suggest typical to above normal
925 mb temperatures. With the available moisture, heat indices above
100 degrees Celsius cannot be ruled out, particularly across urban
and lower elevations of the islands. Hence, residents and visitors
should exercise caution as these levels could impact most
individuals, particularly those without adequate hydration and/or
effective cooling.



&&

.AVIATION...
(18Z TAFS)
Issued at 208 PM AST Tue Jun 9 2026

Mainly VFR conds expected at all TAF sites thru the fcst period.
Trace Saharan dust will persist, but VIS should remain P6SM for the
most part. VCSH/SHRA will continue at times, mainly thru 09/22Z and
again aft 10/13Z. VCTS is psbl at TJPS and TJBQ aft 10/17Z. Brief
MVFR conds psbl in heavier SHRA/TSRA due to reduced VIS and low
cigs. ESE winds 12-15 kt with sea breeze variations and hir gusts
thru 09/22Z, bcmg lgt/vrb to lgt E overnight, then incrg aft 10/14Z.

&&

.MARINE...
Issued at 208 PM AST Tue Jun 9 2026

The Azores high will continue to promote moderate winds tonight
and tomorrow. Then, a tropical wave crossing the Lesser Antilles
on Wednesday and moving across the local islands while interacting
with a deep polar trough on Thursday will enhance the potential
for showers and thunderstorms, especially from Wednesday afternoon
into late Thursday night. Mariners should prepare for stronger
winds and higher seas near thunderstorms.

&&

.BEACH FORECAST...
Issued at 208 PM AST Tue Jun 9 2026

The rip current risk is low for the rest of today and tomorrow.
However, life-threatening rip currents may still occur, especially
near groins, jetties, reefs, and piers.

From Thursday onward, life-threatening rip currents are possible,
first across St Croix, then spreading to the rest of the east and
north-facing beaches in the USVI and PR. Always swim near a
lifeguard and remember to heed the advice of the local beach
patrol and flag warning systems.

&&

.FIRE WEATHER...
Issued at 110 AM AST Tue Jun 9 2026

Drier-than-normal conditions will enhance the availability of
burning fuels along the southern plains of PR and the USVI.
The fire danger fro today is low, as conditions are present.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007-
     008-010>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.
&&

$$

MORNING SHIFT...CAM/CVB
EVENING SHIFT...MNG/MRR

NWS SJU Office Area Forecast Discussion