textproduct: San Juan

KEY MESSAGES

Issued at 212 PM AST Thu Sep 10 2026

- The main risk for the day remains the elevated to significant extreme heat risk. Thus a Heat Advisory is in effect for the US Virgin Islands, Vieques and Culebra. Whereas a Extreme Heat Warning is in effect for mainland Puerto Rico. These conditions are expected to persist throughout the rest of the short term period as a drier pattern settles in.

- Moderate concentrations of Saharan Dust have gradually filtered into the forecast region and will increase to high concentrations later tonight into Friday morning, with the highest concentrations are expected on Friday.

- Passing showers will develop over western Puerto Rico this afternoon,while additional showers are forecast to mover over the US Virgin Islands and the eastern half of PR during the overnight hours.

Short Term(This evening through Saturday)

Issued at 212 PM AST Thu Sep 10 2026

A weak tropical wave moved across the region, increasing TPW values to around 2 inches across Puerto Rico and the U.S. Virgin Islands. Elevated moisture combined with ESE winds supported showers and thunderstorms across southeastern, northeastern, and interior Puerto Rico, as well as the U.S. Virgin Islands. Radar estimates indicate rainfall accumulations of 2 to 4 inches across portions of Cayey, Barranquitas, and Guayama, with 1 to 1.5 inches observed elsewhere across eastern, northern, and interior Puerto Rico. A Flood Advisory for those municipalities was extended through 7:30 AM AST due to the ongoing potential for flooding. As morning convection diminished, heat indices of 100 to 108 degrees Fahrenheit prevailed across the U.S. Virgin Islands, Vieques, and Culebra where a Heat Advisory was issued. Across mainland Puerto Rico, a significant heat risk will prevail, with heat indices above 112 degrees Fahrenheit where the Extreme Heat Warning remains in effect.

For the remainder of today into tonight, passing showers may affect eastern and northwestern Puerto Rico amid moderate concentrations of Saharan dust. As the tropical wave exits, a drier air mass associated with moderate to high concentrations of Saharan dust will spread across the region. The resulting Saharan Air Layer (SAL) will suppress deep convection, with the highest dust concentrations expected from Friday night into Saturday morning. Generally dry conditions will persist through the remainder of the short-term period. However, an upper-level trough north of the forecast area may slightly increase the potential for isolated showers on Saturday. Limited cloud cover and drier conditions will also favor elevated heat risk Friday and Saturday, particularly across urban and coastal areas. Residents and visitors should follow guidance from health officials, limit outdoor activities, and remain adequately hydrated.

Long Term(Sunday through next Wednesday)

Issued at 420 AM AST Thu Sep 10 2026

The surface high-pressure will continue to promote easterly breezy winds across the islands for most of the forecast period. From Saturday night, dust concentrations are expected to diminish as a result of the Saharan Air Layer (SAL) exiting the area. Precipitable water values (PWAT) will briefly reach seasonal values on Sunday and Monday morning, varying between 1.75 to 2.00 inches.

Current model guidance shows a drier air slot moving across the area on Monday afternoon. These drier conditions will persist until Tuesday afternoon, with PWAT values returning to seasonal values by the evening and exceeding two inches by the end of the workweek. A tropical wave is expected to approach the islands following the aforementioned drier air slot. A more robust wave, is anticipated to reach the islands from Thursday night into Friday.

The transition to wetter conditions supported by daytime heating, local effects and the consecutive tropical waves over the CWA could bring an increase to the chance of showers and thunderstorms across the islands, especially through the end of the workweek. This could potentially trigger an elevated flood risk across portions of the islands. We advice residents and visitors to continue monitoring the forecast as adjustments and updates become available.

AVIATION

(18Z TAFS) Issued at 212 PM AST Thu Sep 10 2026

Mainly VFR thru the period. E-ESE winds 14-16 kt with frequent gusts 23-27 kt expected at all terminals, strongest during the afternoon. Saharan dust will maintain HZ with VIS generally 6SM, with brief reductions to 5SM possible.

MARINE

Issued at 212 PM AST Thu Sep 10 2026

A strengthening surface high pressure across the central Atlantic will continue to promote moderate to fresh winds, with locally strong winds and stronger gusts at times, through the next few days. These winds will maintain choppy to locally rough marine conditions, with seas generally around 5 to 6 feet across most waters and local passages, and occasionally up to around 8 feet across the offshore Atlantic waters. Periods of stronger winds and higher seas will remain possible, particularly across exposed waters and passages. Moderate to high concentrations of Saharan dust will also persist across the region during the next few days, resulting in hazy skies and reduced visibility at times. Isolated to scattered showers may move across the waters, but Saharan air will generally limit widespread shower development.

BEACH FORECAST

Issued at 212 PM AST Thu Sep 10 2026

There is a moderate risk of rip currents along most beaches of Puerto Rico and the U.S. Virgin Islands today. Breezy to windy conditions are expected to persist through the next few days, with life-threatening rip currents possible. Beachgoers are urged to exercise caution, especially at beaches without lifeguards.

Moderate to high concentrations of Saharan dust will persist across the region, resulting in hazy skies and reduced visibility at times. Isolated to scattered showers remain possible, but Saharan air will generally limit widespread shower development. Heat will remain an additional concern, and beachgoers should remain hydrated and limit prolonged sun exposure.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Extreme Heat Warning until 5 PM AST this afternoon for PRZ001>011.

Heat Advisory until 5 PM AST this afternoon for PRZ012-013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.