textproduct: San Juan

KEY MESSAGES

Issued at 141 PM AST Fri Jul 10 2026

* Above-normal temperatures will persist through the weekend into early next week, with the greatest heat impacts expected early next week.

* Elevated to critical fire weather conditions will continue through the weekend due to dry soils, low relative humidity, and breezy conditions.

* Moderate to fresh easterly winds, occasionally strong, will persist through early next week, especially across coastal waters and exposed areas.

* Moderate to high concentrations of Saharan dust will continue through the weekend, resulting in hazy skies and reduced air quality before gradually diminishing.

* A tropical wave is expected to increase moisture across the region early next week, leading to a higher potential for showers and isolated thunderstorms.

Short Term(This evening through Sunday)

Issued at 141 PM AST Fri Jul 10 2026

Breezy to windy conditions have dominated this morning and early afternoon across Puerto Rico and the U.S. Virgin Islands as a tight pressure gradient remains in place over the northeastern Caribbean. Surface observations have registered sustained winds of 14 to 18 mph, with frequent gusts up to 30 mph across the islands. Moderate to locally high concentrations of Saharan dust have also resulted in hazy skies. The 12Z TJSJ sounding indicated a strong inversion and a precipitable water value of 1.43 inches, which falls near the 25th percentile for this time of year, highlighting the dry and stable air mass in place. Afternoon temperatures across urban and lower-elevation areas have climbed into the upper 80s to low 90s, producing heat indices generally in the upper 90s to low 100s, with a few locations exceeding 105F. Rainfall has not been observed today, and probably none is expected through the remainder of the afternoon.

By Saturday, a strong Atlantic surface ridge will continue to promote breezy to windy easterly winds across Puerto Rico and the U.S. Virgin Islands. Moderate to locally high concentrations of Saharan dust, combined with a drier-than-normal air mass, will maintain hazy skies and stable weather conditions. Precipitable water values will remain below seasonal normals, while dry mid- level air and a persistent inversion limit vertical cloud development. As a result, only isolated passing showers are expected, mainly overnight and during the morning hours, with little to no afternoon convection.

By Sunday, moisture associated with the next tropical wave will gradually spread into the region, allowing moisture levels to return closer to normal by late in the day. At the same time, an upper-level trough approaching from the northeast will evolve into a cutoff low, providing modest support for increased cloudiness and a few more showers. Even so, atmospheric instability is expected to remain limited, keeping the potential for organized thunderstorms, flooding, and lightning low.

Warm temperatures will persist through the weekend, with the warmest conditions expected across urban, coastal, and lower- elevation areas each afternoon. A limited heat threat is expected to continue on Saturday as breezy conditions provide occasional relief. By Sunday, the heat threat is forecast to become more elevated as increasing moisture allows heat indices to become higher, especially across urban, coastal, and lower-elevation areas. As a result, sensitive individuals may experience greater heat impacts. Residents and visitors are encouraged to stay well hydrated, wear lightweight and light-colored clothing, limit prolonged outdoor activities during the hottest part of the day, and take frequent breaks in the shade or in air-conditioned spaces whenever possible.

Long Term(Monday through Friday)

Issued at 200 AM AST Fri Jul 10 2026

As mentioned in previous discussions a tropical wave is forecast to approach the islands from the east bringing a moister weather pattern by the beginning of the workweek. The latest model guidance continues to suggest mid level relative humidity values ranging between 50 and 75th percentile or near to above normal values for this time of the year. At the same time, the proximity of an upper- level low northeast of the forecast area will maintain slightly cooler mid-level temperatures, around -8 to -9 degrees Celsius at 500 mb, supporting modest instability. With only low concentrations of Saharan dust expected through much of Monday, scattered showers and isolated thunderstorms will be possible. The greatest coverage is expected across the U.S. Virgin Islands and eastern Puerto Rico during the morning, followed by the interior and western sections of Puerto Rico during the afternoon. Locally heavy rainfall may result in ponding of water on roads and in poorly drained areas, with isolated instances of minor flooding.

Saharan dust model guidance suggests that moderate Saharan dust concentrations will approach the islands on Tuesday resulting in hazy skies, periods of reduced visibility, and deteriorating air quality, particularly for sensitive groups. At the same time, the tropical wave will move west of the region while a drier and more stable air mass gradually filters into the area. Precipitable water values are forecast to decrease to near or slightly below normal levels by midweek, while mid-level temperatures gradually warm and relative humidity decreases through the column. As a result, shower activity should become more limited from Tuesday through Friday, with brief passing trade-wind showers during the overnight and morning hours followed by isolated afternoon convection, primarily over the western interior of Puerto Rico. Although localized ponding cannot be ruled out, the overall flooding threat should remain low during the second half of the workweek.

Seasonal to slightly above-normal temperatures are expected through Friday. Combined with sufficient low-level moisture, heat indices will likely exceed 100 degrees Fahrenheit across urban and coastal areas each afternoon, particularly along the northern and southern coastal plains of Puerto Rico and portions of the U.S. Virgin Islands. In addition, the presence of Saharan dust may limit overnight radiational cooling, leading to warmer-than-normal minimum temperatures. Therefore, the heat risk is expected to remain elevated throughout much of the workweek despite the gradual drying trend.

MARINE

Issued at 141 PM AST Fri Jul 10 2026

A broad surface high pressure centered over the central Atlantic, combined with lower pressure over northern South America, will maintain a tight pressure gradient across the northeastern Caribbean through at least early into the weekend. This pattern will support moderate to fresh easterly winds across the regional waters, with occasional strong winds, particularly over the offshore Caribbean waters. These conditions will continue to support choppy to hazardous seas, especially across the offshore Caribbean waters and the Mona Passage. Moderate to high concentrations of Saharan dust will also persist through the weekend, resulting in hazy skies and reduced visibility.

BEACH FORECAST

Issued at 141 PM AST Fri Jul 10 2026

Persistent moderate to fresh easterly winds will continue to generate short-period wind waves, maintaining a moderate risk of rip currents across most beaches of Puerto Rico and the U.S. Virgin Islands through at least Saturday. Life-threatening rip currents remain possible, particularly along beaches exposed to the prevailing easterly winds. Beachgoers should exercise caution, avoid swimming alone, and heed the advice of local beach patrols and posted warning flags.

Moderate to high concentrations of Saharan dust will persist through the weekend, resulting in hazy skies, reduced visibility, and degraded air quality. Warm to hot conditions will continue during the afternoon hours. Sensitive groups should limit prolonged outdoor exposure due to poor air quality, while everyone should stay well hydrated and exercise caution if spending extended periods outdoors. trend.

FIRE WEATHER

Issued at 141 PM AST Fri Jul 10 2026

Today, surface observations have been indicating relative humidity values generally between 50 and 60 percent and frequent easterly wind gusts between 25 and 30 mph, particularly across the southern coastal plains. Persistent rainfall deficits, critically dry fuels continue across much of Puerto Rico, Vieques, Culebra, and St. Croix. A Fire Danger Statement remains in effect today, and additional fire weather products may be needed through the weekend, particularly tomorrow Saturday, stay tuned to the forecast.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...Small Craft Advisory until midnight AST tonight for AMZ711-733- 741.