textproduct: San Juan

KEY MESSAGES

Issued at 1206 PM AST Wed Sep 2 2026

- Afternoon showers and thunderstorms will continue to affect the interior and western Puerto Rico. Ponding of water and localized flooding are possible in urban areas, on roads, and near small streams. Streamers will continue to develop from the islands.

- A Heat Advisory remains in effect for Puerto Rico and the U.S. Virgin Islands through 4 PM AST. Heat will remain one of the primary hazards in the coming days, particularly this next weekend.

- A low risk of rip currents will prevail over the coming days. However, even when the overall risk is low, life-threatening rip currents can occur near groins, jetties, reefs, and piers.

- A weak tropical wave will increase the chances of rain Friday into Saturday. Then, early next week, additional moisture could bring more rainfall chances to the region.

Short Term(This evening through Friday)

Issued at 1206 PM AST Wed Sep 2 2026

A drier and more stable air mass will promote mostly calm weather tonight through Thursday. Precipitable water and mid-level moisture are expected to fall below normal, limiting shower coverage and deeper convective development. A few brief trade wind showers may still affect windward areas, mainly during the nighttime and early morning hours, but significant rainfall impacts are not expected through Thursday.

Weather conditions will begin to change Friday as a weak tropical wave approaches the islands from the east. Moisture will gradually increase during the day, with showers becoming more frequent as the wave gets closer to the US Virgin Islands and Puerto Rico. The highest potential for unsettled weather is expected from Friday night into Saturday, when the deepest moisture moves across the region. Although the wave is expected to remain weak, periods of moderate to locally heavy rainfall and isolated thunderstorms are possible. The main potential impacts will be ponding of water on roads and localized flooding in low lying and poor drainage areas, especially where showers persist or repeatedly affect the same locations. Thunderstorms may also produce lightning and brief gusty winds. Outdoor activities should generally experience favorable conditions through Thursday. Those with plans Friday night into Saturday should be prepared for periods of showers and possible thunderstorms and remain alert for localized flooding where heavier rainfall develops.

Temperatures will remain warm through the period, with daytime highs generally near to slightly above normal. Coastal and urban areas can expect highs in the upper 80s to lower 90s, while temperatures across the interior should generally remain in the upper 70s to lower 80s. The combination of warm temperatures and limited rainfall may result in uncomfortable conditions during the afternoon, particularly through Thursday. Residents and visitors planning prolonged outdoor activities should stay hydrated and take breaks from the heat, and continue to monitor the forecast for any heat-related products that may be issued.

Long Term(Saturday through next Tuesday)

Issued at 1206 PM AST Wed Sep 2 2026

A surface high pressure over the central Atlantic, a mid-level ridge, and the passage of a tropical wave by Tuesday will be the main weather features during the long-term period. On Saturday, the surface high pressure over the central Atlantic will maintain a southeasterly wind flow across the region. Moisture will remain relatively high, with precipitable water values around 1.9 inches. However, at the mid-levels, a ridge near 500 mb will promote warmer temperatures and a strong trade wind cap, providing enough stability to limit the vertical development of showers. At the upper levels, southerly winds around 250 mb will continue to bring periods of upper-level cloudiness across the region. Therefore, despite the available moisture, generally stable conditions should limit widespread rainfall activity. The main concern on Saturday will continue to be the heat threat, particularly across coastal and urban areas.

From Sunday into Monday, the surface pressure gradient will weaken as the high pressure remains over the central Atlantic, resulting in lighter winds across the islands. Winds are expected to become more southerly to southeasterly at the lower levels, while southwesterly winds prevail near 250 mb. Meanwhile, moisture will gradually increase, with precipitable water values approaching 2.0 inches. The combination of weak steering winds, abundant moisture, and local effects should favor afternoon convection, particularly across the interior and northern portions of Puerto Rico. Slow-moving showers could result in locally higher rainfall accumulations, although widespread activity is not anticipated at this time. By Tuesday, weather conditions are expected to become more unstable as the moisture field associated with a tropical wave moves across the region. Model guidance suggests precipitable water values could increase to around the 75th percentile for this time of year, indicating an anomalously moist environment. In addition, an upper- level low is forecast to become positioned near the region, increasing instability aloft and providing better upper-level support for convective development. Upper-level disturbances generally favor enhanced clouds and precipitation by increasing instability and lift. Therefore, Tuesday currently appears to have the greatest potential for more widespread shower and thunderstorm activity, along with an increasing potential for locally heavy rainfall.

AVIATION

(18Z TAFS) Issued at 1206 PM AST Wed Sep 2 2026

Brief periods of MVFR conds will remain possible in and around JSJ/JPS and JBQ in SHRA/TSRA through about 02/20z. Afterwards, VFR conds expected at all TAF sites. Easterly winds at 10kt with sea breeze variations, becoming light and variable overnight.

MARINE

Issued at 1206 PM AST Wed Sep 2 2026

A surface high pressure will continue to build over the far eastern Atlantic and promote gentle to moderate trades through the workweek, with seas between 2 and 4 feet, occasionally 5 feet. The next tropical waves are forecast to reach the local waters and passages by Friday into the weekend, increasing shower and thunderstorm activity and bringing gusty winds and lightning.

BEACH FORECAST

Issued at 1206 PM AST Wed Sep 2 2026

A low risk of rip current is expected to continue throughout the week, likely to become moderate early next week. Aside from rip currents, beachgoers should stay weather alert, particularly each afternoon, due to shower and thunderstorm activity that may move near the western and northern coastal areas of Puerto Rico, producing gusty winds and lightning. Beachgoers must seek shelter whenever they hear thunder.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 4 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory until 4 PM AST this afternoon for VIZ001-002.

AM...None.