textproduct: San Juan

KEY MESSAGES

Issued at 433 AM AST Sat Sep 5 2026

* A wetter pattern is expected through Monday, with more frequent showers and a few thunderstorms. The heaviest rainfall is expected during the afternoon hours, particularly across interior and western Puerto Rico. Locally heavy rainfall could result in ponding of water on roads and flooding in urban and poorly drained areas.

* Periods of showers will also affect eastern Puerto Rico and the U.S. Virgin Islands, particularly during the morning and overnight hours.

* Dangerous heat conditions will continue through the weekend and into Monday. A Heat Advisory is in effect for today, with warm and humid conditions expected to result in significant heat impacts, particularly across coastal and urban areas. Cloud cover and showers may provide some relief at times.

* A low risk of rip currents will prevail across most beaches through the Holiday weekend. However, life-threatening rip currents can still occur where the risk is low, particularly near groins, jetties, reefs, and piers.

Short Term(Today through Monday)

Issued at 433 AM AST Sat Sep 5 2026

During the overnight hours, temperatures remained around 1 to 2 degrees warmer than those observed during the same time frame yesterday. Showers and isolated thunderstorms developed along a narrow northwest-to-southeast oriented band associated with the leading edge of moisture from a broad tropical wave, some of this activity moved over eastern portions of Puerto Rico. For today, above-normal 925-mb temperatures continue to support an elevated heat threat, with conditions potentially approaching Extreme Heat Warning criteria. However, lingering cloud cover could limit daytime heating during the morning hours. Therefore, the Heat Advisory remains in effect, but conditions will be monitored in case an upgrade becomes warranted. For the remainder of the short-term period, increasing tropical moisture will favor a wetter pattern, while strengthening ridging aloft will gradually increase mid-level stability.

For today, moisture will continue to increase as the leading edge of the broad tropical wave moves through the region. Precipitable water values will increase from around 1.7-1.8 inches early this morning to near 2.0 inches by this afternoon, while moisture gradually deepens through the atmospheric column. Some relatively dry air and stability in the mid levels could initially limit convection. Nevertheless, increasing moisture combined with local and diurnal effects should promote afternoon showers and isolated thunderstorms across interior and western/northwestern Puerto Rico, with locally heavy rainfall resulting in ponding of water in roads and poorly drained areas. There is a low chance of urban and small streams flooding, mostly over western Puerto Rico.

Deeper moisture will spread across the region tonight into Sunday, with precipitable water values remaining near or slightly above 2.0 inches and 700-500 mb relative humidity increasing to near or above normal values. This will favor greater shower coverage, with locally heavy rainfall and an increasing flooding threat on Sunday. However, strengthening ridging aloft and decreasing 700-500 mb lapse rates will favor increasing mid-level stability. At the same time, increasing 850-700 mb lapse rates should maintain sufficient low-level instability for convective development. Therefore, convection may become increasingly shallow, with isolated deeper thunderstorms developing where local and diurnal effects provide sufficient lifting.

Abundant moisture will persist into Monday, but strengthening ridging, warming temperatures near 500 mb, and decreasing mid-level lapse rates should further limit deep convection. Favorable low- level lapse rates should still support mainly shallow showers, with isolated deeper convection possible where local effects enhance convergence, mainly over interior and western Puerto Rico. Streamers developing downwind of El Yunque into the San Juan metro area and downwind of the smaller islands cannot be ruled out throughout the period, potentially enhancing localized heavy rainfall. Training showers within these streamers may also result in higher rainfall accumulations over downwind areas. Despite the increasing stability, the above normal columnar moisture will remain capable of producing locally heavy rainfall.

Heat will remain a concern through the period as above-normal 925-mb temperatures and abundant low-level moisture support elevated heat indices. However, the magnitude of the heat threat on Sunday and Monday will depend on cloud coverage and the timing of showers, with increased clouds and earlier convection potentially limiting daytime heating.

Long Term(Tuesday through Saturday)

Issued at 433 AM AST Sat Sep 5 2026

Recent model guidance has trended drier, suggesting limited prospects for meaningful rainfall relief from the ongoing drought and water-supply concerns. Ridging north to northwest of the region should promote generally dry and hot conditions Tuesday. A tropical wave will then approach as the ridge retreats and a trough develops east-northeast of the Caribbean, providing the best opportunity for increased moisture and convection Wednesday into early Thursday. However, uncertainty remains regarding the timing and depth of the moisture. A more extensive dry-air mass should follow the wave and persist through the weekend. Breezy to locally windy east- southeasterly conditions are also expected as high pressure strengthens across the North Atlantic.

Extreme heat will likely remain the primary hazard, particularly Tuesday. Stronger winds, increased cloud cover, and showers may result in slightly lower temperatures Wednesday and Thursday. Although below-normal moisture may limit rainfall coverage and intensity, locally heavy rainfall could produce localized flooding Wednesday into Thursday, while thunderstorms will pose a lightning risk. Nevertheless, widespread or substantial rainfall is not anticipated.

AVIATION

(06Z TAFS) Issued at 433 AM AST Sat Sep 5 2026

Mainly VFR conditions are expected to prevail across all terminals through the fcst period. Passing -SHRA will continue across the USVI and eastern PR terminals overnight into the morning hours. Afternoon convection may result in VCTS and brief MVFR conds at TJBQ after 05/17z, with a PROB30 for -TSRA through 05/21z. Winds light/VRB to calm overnight, becoming E-ESE at 8-15 kt after 05/13z, with sea breeze variations and stronger gusts possible near SHRA/TSRA.

MARINE

Issued at 433 AM AST Sat Sep 5 2026

Light to moderate east to southeast winds will continue this holiday weekend, becoming moderate to fresh by Tuesday as surface high pressure builds across the central Atlantic. These conditions may result in increasingly choppy seas across regional waters and Caribbean Passages. A tropical wave will increase shower and thunderstorm activity across the regional waters late today into Monday, bringing gusty winds and lightning.

BEACH FORECAST

Issued at 433 AM AST Sat Sep 5 2026

The beach forecast remains on track. The latest nearshore buoys continue to report seas between 1 and 3 feet, with breaking waves leading to a low risk of rip currents. Although the risk remains low across all beaches of the islands, beachgoers must pay attention to the beach conditions a isolated life-threatening rip current often occur near jetties, piers, reef, and groins. These conditions should continue this holiday weekend, though strengthening winds should upgrade the risk by Tuesday, becoming moderate. Therefore, the moderate risk is expected across northern and eastern-exposed beaches of the islands on Tuesday, spreading across most beaches during the second part of next workweek. Beachgoers must exercise caution, as life-threatening rip currents are possible along the surf zone. Aside from rip currents, showers and isolated thunderstorm can be expected each afternoon, moving near coastal areas of the islands, bringing gusty winds and lightning. Beachgoers must seek shelter whenever they hear thunder.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ001>013.

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

AM...None.