textproduct: San Juan

KEY MESSAGES

Issued at 252 AM AST Mon Jul 13 2026

* A Heat Advisory is in effect from 10 AM to 5 PM today due to dangerous heat indices expected across coastal and urban areas, as well as the vicinity of Caguas. Please follow the Department of Health recommendations.

* Moisture will gradually decrease throughout the day, limiting the development and coverage of shower activity across the region.

* An area of moderate Saharan dust concentrations will bring hazy skies and limited shower activity. Asthmatic and allergic persons are urged to follow the Health Department recommendations.

* The combination of warm temperatures, low relative humidity, and breezy winds will increase the fire danger risk along the southern plains.

* Breezy conditions will maintain choppy seas for mariners and a moderate risk of rip currents across most local beaches.

Short Term(Today through Wednesday)

Issued at 252 AM AST Mon Jul 13 2026

Overnight conditions remained generally tranquil across the local islands. Variable high cloud cover persisted through the night due to a southerly flow aloft around the 250 mb level. At the surface, Doppler radar detected patches of light showers moving across portions of Puerto Rico, while more organized shower activity remained over the Caribbean waters. Overnight temperatures stayed in the lower 80s across most coastal locations, while the interior and higher elevations cooled into the 70s, with a few isolated mountain sites reporting even cooler readings.

For today, moisture associated with the departing tropical wave will linger through the morning before gradually shifting west of the local area during the afternoon. Similar to yesterday, this moisture and the Saharan dust will result in hazy skies across the region. High clouds may continue through the morning, leading to some variability in daytime heating before gradually thinning later in the day. At the surface, a strong subtropical high centered over the central Atlantic and extending into the northeastern Caribbean will maintain east-southeasterly winds, allowing daytime temperatures to climb into the lower 90s across most coastal and urban areas. Combined with the available morning moisture, these temperatures will produce dangerous heat conditions, especially for vulnerable populations. Therefore, a Heat Advisory remains in effect from 10 AM through 5 PM for the coastal and urban areas of Puerto Rico, including the vicinity of Caguas, Vieques, Culebra, and the U.S. Virgin Islands. The most dangerous period is expected between noon and 2 PM, although residents and visitors are encouraged to follow heat safety recommendations throughout the day, including staying well hydrated, taking frequent 15-minute breaks when working outdoors, and limiting strenuous activities during the hottest hours. In terms of rainfall, the available moisture, forecast soundings, and the presence of Saharan dust suggest another day with only isolated afternoon convective showers across the western interior of Puerto Rico, producing little to no significant rainfall accumulations.

From Tuesday through Wednesday, a strengthening surface high over the central Atlantic will tighten the local pressure gradient, resulting in locally breezy easterly winds across the islands. This pattern will be accompanied of an a drier air mass into the region along plenty of Saharan dust particles. Global guidance [GFS and ECMWF] continues to indicate relative humidity values below 30 percent between the 850 and 500 mb levels, supporting a predominantly dry and stable weather pattern. As a result, warm nighttime temperatures are expected to persist due to the Saharan dust limiting radiational cooling, while abundant daytime sunshine will allow maximum temperatures to develop early in the afternoon and reach the lower to middle 90s across coastal and urban areas. Rainfall chances will remain minimal through the period, with the best opportunity for isolated showers confined to the western interior of Puerto Rico and probabilities generally remaining below 50 percent. Given the continued hot weather, residents and visitors are urged to continue following heat safety guidance to reduce the risk of heat-related illnesses.

Long Term(Thursday through Monday)

Issued at 252 AM AST Mon Jul 13 2026

During the long-term period the best chance to see some rainfall will occur on Thursday as a weak upper-level low interacts with a patch of low-level moisture moving across the islands. The latest model guidance suggest precipitable water and mid-level relative humidity increasing to the 50th and 75th percentile of for this time of the year, providing sufficient moisture to support scattered showers and the chance of a few isolated thunderstorms. While widespread rainfall is not anticipated, moderate showers may produce localized ponding in low-lying and poor drainage areas. Residents with outdoor activities planned for Thursday should remain alert for occasional interruptions from passing showers particularly during the afternoon hour across the western half of Puerto Rico.

At the same time, moderate concentrations of Saharan dust are expected to persist across the region on Thursday, resulting in hazy skies and potentially limiting the coverage of shower activity. People with respiratory illnesses or sensitivities should take the necessary precautions, particularly during prolonged periods outdoors. Saharan dust concentrations are forecast to gradually decrease from late Thursday into the weekend, allowing for improving visibility and air quality.

From Friday through Sunday, an upper-level ridge will strengthen across the region while a drier air mass establishes over the islands. This pattern will promote predominantly stable weather conditions, with only brief, isolated showers expected. Consequently, the weekend is expected to be favorable for most outdoor activities.

Despite the drier conditions, forecast 925 mb temperatures remain above the average for this time of year, supporting warm to hot daytime conditions through the weekend. Residents and visitors are encouraged to stay well hydrated, seek shade where possible, and limit strenuous outdoor activities during the hottest part of the day.

AVIATION

(06Z TAFS) Issued at 252 AM AST Mon Jul 13 2026

VFR conditions will prevail across all TAF sites through the forecast period. Hazy skies associated with Saharan dust will persist across the region, although prevailing visibility is expected to remain P6SM at most terminals. East-southeast winds of 10 to 18 kt with gusts up to 25 kt will develop after 14Z, with lighter winds overnight. Local mountain obscurations are not anticipated, and no significant aviation impacts are expected through the forecast period.

MARINE

Issued at 252 AM AST Mon Jul 13 2026

Surface high pressure will gradually build across the central Atlantic, supporting moderate to locally fresh east to east- southeast winds and moderate chops to locally choppy seas through the workweek. A dense Saharan Air Layer will continue to spread across the region, resulting in hazy skies and reduced air quality, though visibility should generally remain above 5 nautical miles.

BEACH FORECAST

Issued at 252 AM AST Mon Jul 13 2026

The east-to-east-southeast wind flow today promotes a moderate risk of life-threatening rip currents along the north and southeast beaches across Puerto Rico, Vieques and Culebra, and St Croix. Throughout the week, the rip current risk will spread along the north and south beaches in PR, remaining moderate at St Croix. Beachgoers should swim near lifeguards whenever possible, heed beach warning flags, and never swim alone.

An elevated extreme heat risk is also expected along many beaches today and through the first half of the week. Stay well hydrated, seek shade whenever possible, and apply sunscreen to help reduce the risk of heat-related illnesses.

FIRE WEATHER

Issued at 252 AM AST Mon Jul 13 2026

Persistent rainfall deficits, critically dry fuels, and elevated KBDI values continue across much of Puerto Rico and the U.S. Virgin Islands, with the greatest concerns across southern Puerto Rico, Vieques, Culebra, and St. Croix. A drier-than-normal air mass, moderate to locally high concentrations of Saharan dust, and breezy to windy easterly trade winds will continue to support favorable conditions for wildfire growth. For today, RH values may briefly fall to near critical levels during the late morning, particularly across the southern coastal plains. Winds will remain from the east withg southeastern variaiton up to 15 mph and with gusty winds.

Giving the expected conditions, a Fire Danger Statement for today.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ001>005-007-008-010>013.

VI...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for VIZ001-002.

AM...None.