textproduct: San Juan

KEY MESSAGES

Updated at 310 AM AST Sun May 10 2026

* Breezy conditions and a limited heat risk will continue over many coastal and urban areas of the islands.

* Passing showers will continue to move at times along the windward areas of the islands, followed by locally induced afternoon showers over western PR each day.

* Across the U.S. Virgin Islands, breezy conditions and trade wind showers expected at times. Highs reaching the low 90s in urban and coastal areas.

* A moderate risk or rip currents will prevail along the north and east facing beaches of Puerto Rico and the U.S. Virgin Islands.

Short Term(Today through Tuesday)

Issued at 310 AM AST Sun May 10 2026

Mid-level ridging and a generally dry air mass will remain the dominant features across the region through early next week. A strengthening surface high pressure over the central Atlantic will maintain a moderate to fresh easterly to east-southeasterly trade wind flow, with speeds ranging between 15 and 20 knots and occasional higher gusts near coastal areas. Latest satellite- derived and model-simulated precipitable water (PWAT) values are currently between 1.25 and 1.50 inches, which is in the climatological 25th percentile for early May. This lack of moisture, combined with a persistent subsidence inversion noted in recent soundings, will limit vertical development and keep shower activity widely scattered and short-lived. Moving into late Monday and Tuesday, a modest moisture bump is expected, with PWATs climbing towards 1.75 inches, nearing the climatological 50th percentile. However, this moisture is mostly trapped in the lower levels. The mid-to-upper levels remain exceptionally dry, with 700mb-500mb relative humidity frequently dropping below 40%, and overall forecasted lapse rates are poor. Consequently, deep convective development will be suppressed.

However, patches of slightly higher low-level moisture are forecast to drift across the U.S. Virgin Islands and eastern Puerto Rico during the overnight and early morning hours, leading to a few fast-moving passing trade wind showers. By the afternoon, daytime heating and local effects could trigger localized scattered showers over the interior and western municipalities of Puerto Rico, with slightly better coverage possible on Tuesday due to the slight increase in moisture. Overall rainfall accumulations will remain light, as breezy conditions will favor rapid shower movement.

Temperature-wise, heat remains the primary hazard. The 925 mb temperatures show a steady diurnal increase throughout the period, peaking between 22C and 22.5C on Monday and Tuesday afternoons. This persistent warm air mass, combined with available surface moisture, will translate to daytime surface highs in the upper 80s to lower 90s across lower elevations, urban areas, and coastal plains. Residents and visitors can expect elevated heat indices exceeding 100F during peak afternoon heating hours.

Long Term(Wednesday through Sunday)

Issued at 310 AM AST Sun May 10 2026

A drier to seasonal weather pattern is anticipated over the long- term forecast. A broad surface high pressure is expected to linger over the Central Atlantic, promoting E-SE winds through most of the period. Additionally, a mid-level ridge will linger through most of the period, maintaining warmer than normal temperatures (500 mb temperatures fluctuating between -4 and -5 degrees Celsius), promoting subsidence and stability aloft. From Wednesday through Friday, patches of moisture will move from time to time, as the latest model guidance suggests an increase in moisture content (PWAT values between 1.5 and 1.75 inches). Passing showers are likely overnight into the morning hours over windward sections of the islands, with shallow afternoon convection in the western/northwestern section of Puerto Rico. Although shower activity may not lead to significant flooding impacts, localized areas can expect puddles over the roads and may become hazardous for drivers. By Saturday and Sunday, another surface high pressure moving over the Western Atlantic, and the high over the Central Atlantic may induce a col region north of the region, weakening the pressure gradient and winds. Due to local effects, combined with diurnal heating and sea breeze convergence, afternoon showers, particularly over interior and western Puerto Rico, may become stationary, increasing flooding potential. Ponding of water over roadways and poorly drained areas can be expected given these conditions, along with minor flooding. Isolated thunderstorms, on the other hand, cannot be ruled out.

Under an east-southeasterly wind pattern, warmer-than-normal temperatures are expected during the long-term forecast. Combined with the available moisture content, heat indexes will likely surpass 100 degrees and even meet Heat Advisory Criteria. Residents and visitors are encouraged to stay tuned for further updates, as these warm to hot conditions can affect most individuals sensitive to heat.

Based on the latest NASA DUex product, minor concentrations of SAL may reach the CWA on Wednesday, but may affect people sensitive to these particles.

AVIATION

(06Z TAFS) Issued at 310 AM AST Sun May 10 2026

Mainly VFR conditions expected to prevail across all terminals through the forecast period. However, trade wind SHRA will move at times across area terminals, causing mostly VCSH and brief periods of -RA and MVFR cigs. Winds will continue 15-20 kt from the east to southeast with NE sea breeze variations at TJSJ/TJBQ.

MARINE

Issued at 310 AM AST Sun May 10 2026

A strengthening surface high pressure over the central Atlantic will promote moderate to locally fresh east-to-southeast winds across the regional waters through early this week. Choppy marine conditions are expected with sustained winds of 15 to 20 knots with occasional higher gusts. Seas will range between 3 and 5 feet, with occasional seas up to 6 feet. Small craft are urged to exercise caution across most local waters.

BEACH FORECAST

Issued at 310 AM AST Sun May 10 2026

A moderate risk of rip currents will continue along the north, east, and southeast-facing beaches of Puerto Rico, Culebra, Vieques and St. Croix due to breezy winds. Across these beaches, life- threatening rip currents are possible in the surf zone, and beachgoers should exercise caution. A similar pattern is expected to persist into next week as breezy conditions persist. A low risk of rip currents will persist across the southern and western beaches of Puerto Rico, however, life- threatening rip currents can still occur near groins, jetties, reefs, and piers.

A small long-period northeasterly swell is expected to arrive by mid- week and spread across local waters. This will result in breaking waves of up to 4 to 5 feet, occasionally higher at times. For additional information, visit weather.gov/beach/sju.

FIRE WEATHER

Issued at 310 AM AST Sun May 10 2026

Breezy easterly trade winds, coupled with a drying air mass, will lead to elevated fire weather concerns today, particularly across the southern coastal plains of PR. Latest soil moisture and fuel assessments indicate Keetch-Byram Drought Index (KBDI) values are currently ranging from 501 to 669 along the southern coast. This indicates significant soil moisture deficits and highly receptive 10-hour fuels, particularly in southwestern PR. Minimum relative humidity values are forecast to drop into the low 50s.

Concurrently, a tight local pressure gradient will sustain breezy easterly surface winds of 16 to 22 mph, with gusts up to 30 mph. The combination of receptive fuels, strong and gusty winds, and lowering relative humidity will result in an elevated fire danger along the southern coastal plains.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...None.