textproduct: San Juan

KEY MESSAGES

Issued at 132 PM AST Mon May 18 2026

* An upper-level trough northwest of the islands will support the development of showers and isolated thunderstorms, particularly during the afternoon hours across western Puerto Rico. A limited to elevated flooding risk will accompany the strongest activity.

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

* Across the U.S. Virgin Islands, passing showers are expected mainly during the overnight and early morning hours, followed by warm conditions during the daytime hours.

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

* A moderate risk of rip currents will persist through the week, mainly along the north, east, and south-facing beaches of Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands.

Short Term(This evening through Wednesday)

Issued at 132 PM AST Mon May 18 2026

Variable weather conditions prevailed across the region today under mostly sunny to partly cloudy skies. A few passing showers moved across portions of eastern Puerto Rico and the U.S. Virgin Islands during the early morning hours, leaving minimal rainfall accumulations. Doppler radar and satellite observations showed clouds developing across the interior by mid-morning, which then increased in coverage during the afternoon. Maximum temperatures reached the upper 80s to low 90s along coastal and urban areas, while ranging from the low to mid-80s in the higher mountains. Breezy to locally windy conditions persisted today with easterly winds of 15 to 20 mph, accompanied by higher gusts and sea breeze variations.

For the rest of the afternoon, showers will develop across the interior and move toward the western portions of Puerto Rico. While a few isolated showers cannot be ruled out across these areas, particularly from San Sebastian to Anasco, the rest of the region will experience mainly fair weather as a patch of drier air continues to filter in from the east.

Looking ahead, an amplifying upper-level trough to the west- northwest of the region will promote increased instability and a higher frequency of showers. However, the presence of drier air patches in the mid-levels may help inhibit some of this activity. Fast-moving showers will continue to be steered toward windward sectors, resulting in periods of variable, showery weather that could cause ponding of water on roads and poorly drained areas, with a minor chance of urban and small stream flooding. Meanwhile, a high- pressure system strengthening north of the area will maintain a tight pressure gradient across the region. Consequently, breezy to locally windy conditions are anticipated to persist through at least the upcoming weekend.

Warm to hot temperatures will remain through the rest of the period, potentially leading to heat indices over 100 degrees Fahrenheit across urban and coastal areas of Puerto Rico and the U.S. Virgin Islands. This heat could pose a risk to sensitive individuals, therefore, residents and visitors are encouraged to stay hydrated, seek shade, and monitor local conditions to ensure safety during peak heating hours.

Long Term(Thursday through Monday)

Issued at 440 AM AST Mon May 18 2026

Model guidance has remained fairly consistent through the long-term period, supporting a persistent late spring weather pattern across the local islands and surrounding waters through the Memorial Day weekend. Broad surface high pressure over the central Atlantic will maintain moderate to fresh easterly winds, becoming breezy to locally windy at times late in the week and during the weekend. Moisture embedded within the trade wind flow will continue to fluctuate between drier and wetter periods, with some moisture patches lingering longer from Friday onward and supporting a gradual increase in shower activity. Minor traces of Saharan dust will occasionally filter across the area with little impact expected. Temperatures will remain seasonably warm to hot, while marine and beach conditions gradually deteriorate through the weekend with increasing rip current and marine hazards.

At upper levels, the area will remain between troughing over the western Atlantic and ridging to the southeast, with the trough gradually shifting closer to the region late in the period. This pattern will support periods of enhanced upper-level winds and more favorable conditions for afternoon convection by the weekend and early next week. Passing showers will continue across windward areas during the overnight and morning hours, followed by afternoon showers and isolated thunderstorms mainly across interior and western Puerto Rico. Localized flooding concerns may gradually increase through the holiday weekend, especially in urban and poor drainage areas, along with lightning and gusty winds in the strongest activity.

AVIATION

(18Z TAFS) Issued at 132 PM AST Mon May 18 2026

Mainly VFR conds are expected across all TAF terminals during the next 24 hrs. However, brief rounds of SHRA/TSRA could result in VCSH/VCTS and low CIGs at TJBQ thru 18/23Z. Breezy to windy conditions from the E to SE with higher gusts and sea breeze variations will persist thru 18/22Z-23Z, becoming light and variable overnight around 5 to 10 kts.

MARINE

Issued at 132 PM AST Mon May 18 2026

A strong surface high pressure over the western Atlantic will promote moderate to fresh easterly trade winds throughout the forecast period as it continues to shift into the central Atlantic. These breezy conditions will maintain choppy to rough seas, particularly across the offshore Atlantic waters and local passages. A Small Craft Advisory remains in effect for the offshore Atlantic waters through at least Tuesday afternoon. Mariners should avoid navigating in hazardous conditions and exercise caution across the rest of the local waters. Passing showers will continue across the regional waters, especially during the overnight and early morning hours. Isolated thunderstorms may develop during the afternoon and early evening across the northwestern waters of Puerto Rico.

BEACH FORECAST

Issued at 132 PM AST Mon May 18 2026

A moderate risk of life-threatening rip currents will continue 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. The highest risk will remain along exposed beaches. Beachgoers should exercise caution when entering the water, as dangerous rip currents are possible within the surf zone.

Afternoon thunderstorms are also possible across western Puerto Rico each day. Residents and visitors should seek shelter immediately if thunder is heard.

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

FIRE WEATHER

Issued at 132 PM AST Mon May 18 2026

A slight increase in moisture on Tuesday may prevent RH values from remaining above 55%; 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 Tuesday for AMZ711.