Since 2001 providing the latest information on tropical cyclone activity in the Atlantic Basin and the weather conditions in Puerto Rico.

Local Weather Conditions

 

National Weather Service Today's Weather Impact Levels

National Weather Service Forecast for: San Juan, Puerto Rico  

Updated: 9:10 pm AST May 21, 2025

Hazardous Weather Outlook
Tonight

Tonight: Isolated showers before 3am.  Partly cloudy, with a low around 76. East southeast wind 7 to 9 mph.  Chance of precipitation is 10%.
Isolated
Showers

Lo 76 °F
Thursday

Thursday: Isolated showers, then scattered showers and thunderstorms after 3pm.  Mostly sunny, with a high near 91. East wind 8 to 15 mph.  Chance of precipitation is 40%.
Scattered
Showers

Hi 91 °F
Thursday
Night
Thursday Night: Scattered showers, mainly between 9pm and midnight.  Partly cloudy, with a low around 77. East wind around 9 mph.  Chance of precipitation is 50%.
Scattered
Showers then
Isolated
Showers
Lo 77 °F
Friday

Friday: Showers likely, mainly before 9am.  Partly sunny, with a high near 89. East wind 10 to 16 mph, with gusts as high as 21 mph.  Chance of precipitation is 60%.
Showers
Likely then
Scattered
Showers
Hi 89 °F
Friday
Night
Friday Night: Isolated showers.  Partly cloudy, with a low around 77. East wind around 10 mph.  Chance of precipitation is 10%.
Isolated
Showers

Lo 77 °F
Saturday

Saturday: Isolated showers.  Mostly sunny, with a high near 90. East wind 11 to 17 mph, with gusts as high as 22 mph.  Chance of precipitation is 20%.
Isolated
Showers

Hi 90 °F
Saturday
Night
Saturday Night: Partly cloudy, with a low around 77. East wind around 10 mph.
Partly Cloudy

Lo 77 °F
Sunday

Sunday: Mostly sunny, with a high near 89. East wind 13 to 15 mph, with gusts as high as 20 mph.
Mostly Sunny

Hi 89 °F
Sunday
Night
Sunday Night: Scattered showers.  Partly cloudy, with a low around 77. East wind 8 to 10 mph.  Chance of precipitation is 30%.
Scattered
Showers

Lo 77 °F

National Weather Service Forecast Details

 

GRLevel3 Radar

  [10/10
GRLevel3 radar from NWS station TJUA

Day 1 rainfall

Day 2 rainfall

Day 3 rainfall

037
FXCA62 TJSJ 211901
AFDSJU

Area Forecast Discussion
National Weather Service San Juan PR
301 PM AST Wed May 21 2025

.KEY MESSAGES...

* Afternoon showers and thunderstorms are expected daily across
  the Cordillera Central of Puerto Rico, creating a limited to
  elevated risk of flooding rains.

* The warm to hot period will extend into tomorrow, Thursday, but
  will linger, in less magnitude, throughout much of the forecast
  period.

* An unstable weather pattern may return by early next week.

&&

.SHORT TERM...Tonight through Saturday...

Skies remained mostly clear today across Puerto Rico and the U.S.
Virgin Islands, allowing for strong diurnal heating. As a result,
maximum heat index values reached between 100 and 110F,
particularly across urban and coastal areas. Winds prevailed from
the east-southeast at 5 to 15 mph, with locally higher gusts
observed near passing showers. Doppler radar detected isolated
thunderstorm development downwind of La Sierra de Luquillo during
the early afternoon, followed by additional convective activity
along the Cordillera Central later in the day, particularly from
Villalba to Las Maras.

Today`s atmospheric sounding reveals a favorable setup conducive
to convective development across Puerto Rico, particularly in the
interior and northwestern sectors of the island due to the east-
southeast wind flow. One of the most noteworthy features is the
presence of steep lapse rates at both low and mid-levels of the
atmosphere. This stability parameter, combined with the wind
flow, the island`s topography, diurnal heating, and sea breeze,
will act as a lifting mechanism enhancing convective initiation
during the afternoon hours. Given the instability, moisture, and
favorable wind flow, there is an elevated risk for localized
flooding, especially in areas prone to poor drainage or where
soils are already saturated from recent rainfall events.

As the afternoon progresses into the evening hours, rain activity
will slowly dissipate. By sunset, most of the shower and
thunderstorm activity is expected to wane, allowing for clearing
skies and relatively calm weather conditions overnight. These
clear and calm conditions will promote nighttime radiational
cooling, with low temperatures dropping into the low 70s along the
coastal zones, while the mountainous interior could see
temperatures dip into the mid-60s, providing a cooler and more
comfortable night.

Although the warming/hot trend is forecast to wane by Friday,
there is a moderate to high confidence that we will observe
another Heat Advisory due to above normal values tomorrow,
Thursday, between 10 am and 4 pm AST. Generally, the typical May
rain pattern will hold through the short-term period, with calm
conditions during the mornings and overnight hours, without ruling
out one or two passing showers. Then, afternoon convection will
return mainly due to the diurnal heating, local effects, and sea
breeze.

.LONG TERM...Saturday through Wednesday...

The weekend will begin with a typical seasonal weather pattern,
as near-normal to slightly below-normal moisture levels combine
with marginal instability aloft, associated with weak ridging over
the northeastern Caribbean. Shower activity will follow the
characteristic diurnal pattern, with passing showers affecting
windward coastal areas of the islands during the night and early
morning hours. This will be followed by afternoon convective
activity, driven by surface heating, sea breeze convergence, and
orographic lifting over the interior and western portions of
Puerto Rico.

A few isolated thunderstorms may develop at times during this
period, but they are expected to be brief. Additionally, breezy
conditions will result in fast-moving showers, limiting rainfall
accumulations in any specific area. At most, a limited flooding
risk is expected, potentially leading to ponding on roadways and
poor drainage areas, with very localized urban and small stream
flooding. A limited excessive heat risk will also persist through
the weekend across urban and coastal areas, primarily affecting
heat-sensitive individuals, especially those outdoors without
effective cooling or adequate hydration.

Uncertainty persists by early next week due to the interaction
between a deepening upper-level trough to the west of the forecast
area and an approaching tropical wave from the east, currently
located near 28.5W. The timing and placement of these synoptic
features remain fairly consistent across model guidance, with the
latest runs positioning the trough axis over Hispaniola between
Tuesday and Wednesday. This places our area on the favorable
(eastern) side of the trough. At the same time, the tropical wave
is expected to begin lifting northward, moving over or near our
region. However, the most active portion of the wave now appears
to be slightly farther west compared to previous model runs.
Despite this shift, well above-normal moisture and increased
instability aloft will be present across the forecast area,
increasing the potential for numerous showers and thunderstorms.
This could lead to an increased flooding threat for Puerto Rico
and the U.S. Virgin Islands.

However, the Caribbean may be under the influence of the
suppressing phase of the MJO, which is indicative of reduced
upper-level divergence and decreased favorability for deep
convective activity. In fact, the latest CPC Global Tropics
Hazards Outlook assigns a 50% to 65% probability of below-average
rainfall across the northeastern Caribbean. This introduces
additional complexity to the forecast. Nevertheless, it is
important to continue monitoring the situation, as there remains a
chance for increased moisture convergence and instability to
result in a heightened flooding risk by early next week.

&&

.AVIATION...
VFR conditions will continue across all TAF sites. However,
SHRA/TSRA will develop along the Cordillera Central through
21/23z, creating mountain obscuration and possibly affecting JBQ,
where TEMPOs are in place. Winds will continue from the E-ESE at
10-15 kt but locally higher near TSRA/SHRA, and with sea breeze
variations, winds will become calm to light and variable after
21/23z. Winds will turn more from the E at around 15 kt tomorrow
after 22/13z. We expect a similar weather pattern tomorrow.

&&

.MARINE...
Light to gentle easterly winds continue today across most local
waters. However, a building surface high pressure over the central
Atlantic will bring moderate to locally fresh easterly trades tonight
through the weekend. Isolated thunderstorms will continue to develop
across the regional waters, particularly across the northern and
western coastal waters of Puerto Rico each afternoon.

&&

.BEACH FORECAST...

Beachgoers, the risk for rip currents is low tonight and
throughout the rest of the week. However, please exercise caution
as life-threatening rip currents often occur in the vicinity of
groins, jetties, reefs, and piers.

&&

.SJU WATCHES/WARNINGS/ADVISORIES...
PR...Heat Advisory until 4 PM AST this afternoon for PRZ001-003-005-
     007-008-010-011.

VI...None.
AM...None.
&&

$$

Day shift...CAM/GRS
Evening crew...LIS/MRR

NWS SJU Office Area Forecast Discussion

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