textproduct: San Juan

KEY MESSAGES

Issued at 240 PM AST Sun Sep 6 2026

* The heat threat will remain elevated to significant across the islands during the upcoming days, as moisture remains across the area and warm temperatures, combined with limited cloud cover, increase heat index values along coastal and urban areas.

* Afternoon showers across western sections and portions of the eastern islands will remain in the forecast, widespread flooding threat is not expected.

* A low risk of rip currents will remain along all coastal areas for the rest of today into Monday, increasing to moderate by Tuesday along the northern coastal areas of Puerto Rico, Culebra, Vieques, and the U.S. Virgin Islands.

* Model guidance suggests the presence of Saharan dust particles across the islands by Tuesday.

Short Term(This evening through Tuesday)

Issued at 240 PM AST Sun Sep 6 2026

Variable weather conditions persisted during the morning hours, with upper-level cloudiness dominating all of the CWA. As the day progressed, warm temperatures were observed across the area, with maximum temperatures in the low 90s along the coast and heat indices quickly reaching 100 and surpassing 108 degrees across some coastal areas. As of 12 PM AST, satellite and radar imagery spotted some areas with increasing cloudiness and showers affecting mostly the northeastern sections of Puerto Rico, spreading across the San Juan metro area. At 1 PM AST, showers developed across the interior central sections, affecting Morovis, Ciales & Manati were a flood advisory was issued due to rainfall accumulations of 1 to 2 inches. For the rest of the afternoon, showers are forecast to develop across the northwestern interior over the municipalities in the vicinity of San Sebastian.

On Sunday, the broad surface high pressure over the central Atlantic will maintain a southeasterly wind flow across the CWA. Under this wind pattern, moisture will remain over the islands, with precipitable water values around 1.9 inches. Although the available moisture may support an increase in shower activity, the presence of a ridge near 500 mb will promote warmer temperatures aloft and a strong trade wind cap, providing enough stability to limit the vertical development of showers. Additionally, the peripheral area of an upper-level low will remain near the region, resulting in some upper-level cloudiness due to the southerly winds. However, this feature will quickly be replaced by an upper- level high. Therefore, despite the available moisture, generally stable conditions should limit widespread rainfall activity, with showers mainly expected during the early afternoon hours across the San Juan metropolitan area and northwestern Puerto Rico. The main concern on Saturday will continue to be the heat threat, particularly due to the high moisture content across the area. This moisture will maintain elevated dew points, which will contribute to higher heat indices across the islands. Heat indices are expected to range from 100 to 111 degrees across coastal and urban areas, while values between 100 and 106 degrees are expected across the mountainous sections.

From Monday into Tuesday, weather conditions are expected to remain very similar, with a broad surface high pressure extending from the central into the western Atlantic and maintaining a southeasterly wind flow across the region. Under this wind pattern, plenty of tropical moisture will continue to move across the islands, maintaining a moist environment throughout the period. Model guidance continues to suggest moisture values around the 75th percentile for this time of year, indicating above-normal moisture content across the region. This available moisture will support periods of passing showers across the local waters and portions of eastern Puerto Rico and the U.S. Virgin Islands during the overnight and morning hours, followed by additional afternoon shower development mainly across interior and northwestern Puerto Rico due to the combination of daytime heating and local effects. However, the main limiting factor for widespread and organized shower activity will continue to be a mid-level ridge established across the region. This feature will maintain warmer temperatures and stable conditions near the 500-mb level, limiting the vertical development of showers despite the abundant low-level moisture. Therefore, most of the activity should remain relatively shallow and driven mainly by local and diurnal effects, although isolated deeper convection cannot be ruled out where sufficient convergence occurs. Similar to previous days, the combination of abundant moisture and warm temperatures will maintain elevated heat indices across the islands, particularly across coastal and urban areas during the late morning and afternoon hours.

Long Term(Wednesday through next Saturday)

Issued at 424 AM AST Sun Sep 6 2026

A surface high-pressure will move closer to the northeastern Caribbean, tightening the pressure gradient and resulting in breezy to locally windy east-southeasterly winds, especially along coastal and exposed areas. A weak tropical wave will move through the region Wednesday, with residual moisture persisting into Thursday. Precipitable water values are expected to increase to 2.1 to 2.3 inches, just above the 75th percentile for this time of year, and the 500 mb temperatures are expected to decrease to near -6 to -7 degrees Celsius, supporting an increase in shower and thunderstorm activity. However, the breezy conditions should limit the flood potential, with little relief expected for the ongoing drought and water-supply concerns.

A drier air mass, accompanied by low concentrations of Saharan dust, will spread across the region Friday and Saturday. Precipitable water values will decrease to around 1.5 inches, nearly two standard deviations below normal, favoring mostly stable and warmer conditions. Some uncertainty remains Friday, as the ECMWF maintains higher moisture across the region.

By Sunday, an upper-level low and associated lower-level disturbance may move closer to the northeastern Caribbean, gradually increasing moisture and instability. Precipitable water values are expected to rise to 1.6 to 1.8 inches, closer to climatological normals, while cooler 500-mb temperatures and more favorable mid-level conditions could further enhance instability and shower and thunderstorm development, especially in the afternoon along the western interior and northwestern quadrant.

Overall, the tropical wave may provide some temporary relief from the heat Wednesday and Thursday, but warmer conditions are expected to return late in the week and into the weekend, with limited to elevated heat risk persisting through the period.

AVIATION

(18Z TAFS) Issued at 240 PM AST Sun Sep 6 2026

Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, locally induced SHRA/TSRA may result in tempo MVFR conditions at TJSJ/TJBQ thru 06/21z. Elsewhere, mostly VCSH/VCTS expected. The 06/12z TJSJ sounding indicated SE winds up to 14 kt blo FL025. Sea breeze variations and stronger gusts will continue at times through late this afternoon. Light and variable winds are expected overnight.

MARINE

Issued at 240 PM AST Sun Sep 6 2026

Light to moderate southeasterly winds will prevail through tomorrow (Monday). Winds will strengthen and become moderate to fresh from Tuesday onward as a surface high pressure builds across the central Atlantic, resulting in choppy seas up to 6 feet and east winds up to 20 knots across most offshore waters and passages. Lingering moisture from a tropical wave will continue to bring scattered showers and isolated thunderstorms across the regional waters through Monday.

BEACH FORECAST

Issued at 240 PM AST Sun Sep 6 2026

A low risk of rip currents is expected to continue through the rest of the Holiday weekend across all beaches of the islands. However, even when the risk is low, life-threatening rip currents often occur near jetties, piers, reef, and groins. By Tuesday, the risk will increase to moderate, as winds increase and seas gradually build to around 4 or 5 feet across the coastal waters of the islands. The moderate risk is expected mainly across the northern and eastern beaches of the islands, and spreading across most beaches during the half of the workweek.

Another beach hazard will be the heat. Beachgoers should remain hydrated and limit prolonged sun exposure. Additionally, gusty winds and lightning due to afternoon showers and isolated thunderstorms, particularly across the western beaches of Puerto Rico. Beachgoers should seek shelter whenever they hear thunder.

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.