textproduct: San Juan

KEY MESSAGES

Issued at 126 PM AST Thu Sep 3 2026

* Showers and thunderstorms are expected to continue over the interior and western portions of PR through the rest of the afternoon hours.

* A weak tropical wave will bring an increase in showers and a few thunderstorms by early Friday across the USVI and later in the day across PR. Ponding of water in poor drainage areas and localized minor flooding are possible.

* Hot conditions will continue through the next several days, particularly across coastal and urban areas and lower-elevation valleys. Dangerous heat conditions are possible this weekend.

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

Short Term(This evening through Saturday)

Issued at 126 PM AST Thu Sep 3 2026

Brief showers filtered over the eastern region of Puerto Rico during the morning hours with minimal rainfall accumulations. During the day temperatures along the coastal areas remained in the upper 80s to low 90s, while across the mountains they remained in the upper 70s to low 80s degrees Fahrenheits. Heat indices were in general from the high 90s to the low 100s degrees Fahrenheit along most coastal and urban areas.

For the rest of this afternoon, expect showers and thunderstorms to develop due to local effects, daytime heating, and marginal instability can not be ruled out, especially over interior and western portions of Puerto Rico during the afternoon hours. Nevertheless, their effects should remain limited.

On Friday, we anticipate a gradual transition into a slightly wetter pattern as a weak tropical wave approaches Puerto Rico and the US Virgin Islands. Model guidance suggests and increase in precipitable water (PWAT) values up to 2 inches. These conditions may enhance the development of passing showers and thunderstorms across the US Virgin Islands and eastern Puerto Rico in the morning hours. In the afternoon, the humidity along with local effects may favor the development of showers and thunderstorms over the interior and western regions of Puerto Rico. However, the effects associated with these humid conditions will remain limited due to mid-level stability inhibiting the vertical development for significant convection. Lingering moisture on Saturday will produce similar conditions across the islands.

Overall, we forecast limited ponding of water, lightning, and heat risk throughout the period. During the peak daytime heating, we recommend limiting outside activities and remaining hydrated. Those with outdoor plans are encourage to remain vigilant for any weather updates as the weak tropical waves approaches the region.

Long Term(Sunday through next Wednesday)

Issued at 126 PM AST Thu Sep 3 2026

A seasonal weather pattern is expected early next week, transitioning to drier-than-normal by the end of the period. A surface high pressure building over the Central Atlantic will likely maintain E-SE winds throughout most of the period, gradually strengthening and bringing breezy to windy conditions by the latter part of the next workweek. Abundant moisture content across the CWA during the first part of next workweek, particularly on Tuesday into Wednesday as a tropical wave approaches the Caribbean Basin. Based on the latest model guidance, PWAT values may vary between seasonal and above-normal values (between 1.8 and 2.2 inches), with low- to mid-level moisture content reaching near above climatological normal (above 60%). In terms of instability, a mid- to high-level ridge positioned across the region may not favor deeper convection, as mid- level temperatures seem warmer than normal (between -5 and -6 degrees Celsius) and heights, bringing subsidence and instability aloft. Nevertheless, the combination of daytime heating, local effects, and high moisture content should enhance afternoon convection, with showers and thunderstorms moving over the mountain ranges into western/northwestern Puerto Rico each afternoon, increasing flooding threat. Typical showers may move from time to time across windward sections of Puerto Rico and the U.S. Virgin Islands. Rainfall accumulations will likely lead to ponding of water over roadways and poorly drained areas, with the highest chance of urban and small stream flooding on Tuesday. Drier-than- normal conditions can be expected by late Thursday, with PWAT values plummeting to well below normal for this time of the year (around 1.5 and 1.6 inches), though available moisture and the vicinity of an upper-level trough weakening the mid-to-high level ridge and could still enhance afternoon convection.

Due to the moist southeasterly wind flow, above-normal temperatures are expected during the early part of the long term period, with the 925 mb temperatures above two standard deviations for this time of the year. Therefore, elevated to significant heat risk is expected throughout the forecast period, Sunday being the hottest day.

AVIATION

(18Z TAFS) Issued at 126 PM AST Thu Sep 3 2026

Mainly VFR conds are expected to prevail across all terminals through the fcst period. However, tempo MVFR conds are possible at TJBQ thru 03/22z due to locally induced SHRA/TSRA. A weak tropical wave should increase SHRA and iso TSRA from the Anegada Passage into the USVI/Eastern PR terminals btw 04/10-15z. ESE winds will continue 10-15 kt with stronger gusts and sea breeze variations at TJSJ/TJBQ thru at least 03/21z, then becoming light and variable overnight.

MARINE

Issued at 126 PM AST Thu Sep 3 2026

Light to moderate east to southeast winds are expected to prevail in general through at least early next week. By then, strengthening of the surface high pressure over the central Atlantic will promote moderate to fresh trades through the rest of next week. A weak tropical wave is expected to bring scattered showers and isolated thunderstorms on Friday, followed by another tropical wave with an increase in shower and thunderstorm activity from Sunday into Monday.

BEACH FORECAST

Issued at 126 PM AST Thu Sep 3 2026

At least through midweek next week, a low risk of rip currents is expected to prevail across most beaches, as seas remain between 1 and 3 feet across the coastal waters of the islands. However, even when the risk for rip currents is low, life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. Beachgoers are encouraged to enjoy generally favorable beach conditions while remaining aware of isolated rip currents and changing weather conditions. Afternoon thunderstorms with cloud to ground lightning are expected each day across the western coastal areas of Puerto Rico.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None.

VI...None.

AM...None.