textproduct: San Juan

KEY MESSAGES

Issued at 327 AM AST Thu Sep 3 2026

* Additional showers will move across eastern Puerto Rico during the morning, followed by stronger afternoon showers and thunderstorms due to lingering moisture and local effects.

* A weak tropical wave will bring an increase in showers and a few thunderstorms Friday into Saturday. Some areas could receive locally moderate rainfall.Ponding of water and localized flooding are possible in urban areas, on roads, and near small streams.

* Hot conditions will continue through the next several days, particularly across coastal and urban areas and lower-elevation valleys. A Heat Advisory is in effect today, with more dangerous heat conditions possible this weekend.

* A low risk of rip currents will continue over the next few days. However, dangerous rip currents can still occur, particularly near groins, jetties, reefs, and piers.

Short Term(Today through Saturday)

Issued at 327 AM AST Thu Sep 3 2026

During the overnight hours, passing showers moved across the local waters and portions of the windward coastal areas. However, showers remained brief and generally light, leaving minimal rainfall accumulations.

A drier air mass will continue to filter into the region today, with precipitable water values gradually decreasing through the day and potentially reaching around 1.4 inches by this evening. Low- to mid- level moisture will also decrease considerably. Although the reduction in available moisture should limit the overall coverage and intensity of convection, marginal instability combined with daytime heating and local effects could still promote the development of showers and isolated thunderstorms across the interior and western portions of Puerto Rico this afternoon. Nevertheless, activity should remain relatively limited, with significant rainfall impacts generally not anticipated.

Conditions will change slightly late tonight into Friday as a weak tropical wave approaches the islands from the east. Moisture will increase with precipitable water values rebounding to around 2.0 inches and mid-level moisture increasing to near or slightly above climatological normals. As a result, an increase in passing showers is expected across the U.S. Virgin Islands and eastern Puerto Rico during the morning hours, followed by showers and isolated thunderstorms developing across the interior and western portions of Puerto Rico during the afternoon. Despite the increase in moisture, instability will remain marginal to modest, limiting the potential for widespread or particularly vigorous convection. Therefore, the main effect of the tropical wave will be an increase in shower coverage compared to today, with locally moderate rainfall possible with the stronger activity.

Moisture will remain elevated into Saturday, with precipitable water values generally around 1.9 to 2.0 inches and sufficient low- to mid- level moisture remaining across the region. However, warmer temperatures near 500 mb and slightly weaker mid-level lapse rates should increase stability aloft, limiting the vertical development and intensity of convection. Passing showers will remain possible across windward areas during the morning, followed by locally induced afternoon showers and isolated thunderstorms, mainly across the interior and western/northwestern portions of Puerto Rico. Overall, activity should remain relatively limited despite the available moisture, with locally moderate rainfall possible with the strongest showers.

Heat will remain one of the primary hazards throughout the short- term period. A Heat Advisory is in effect across Puerto Rico and the U.S. Virgin Islands today, with heat index values expected to reach advisory criteria across many coastal and urban areas, as well as some lower-elevation valleys. Similar conditions are likely on Friday, although increased cloud and shower coverage may provide some localized relief. By Saturday, increasing low-level moisture combined with the persistently warm air mass could result in more oppressive conditions, with Extreme Heat Warning criteria possible in some areas, particularly across coastal and urban areas and lower- elevation valleys that experience prolonged periods of sunshine.

Long Term(Sunday through Thursday)

Issued at 327 AM 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

(06Z TAFS) Issued at 327 AM AST Thu Sep 3 2026

Mainly VFR conds expected across all terminals through the fcst period. Brief VCSH possible at TJSJ/TIST/TISX early morning, but no sig operational impacts expected. SHRA/TSRA development is possible aft 03/15z across interior and W PR, with brief MVFR conds possible in and around TJBQ/TJPS. E winds at 6-10 kt overnight, increasing to 10-15 kt after 03/13z with sea breeze variations, then becoming light overnight.

BEACH FORECAST

Issued at 327 AM AST Thu Sep 3 2026

A low risk of rip currents is expected to continue through at least early next week, with generally favorable beach conditions expected. However, isolated rip currents can still occur, particularly near jetties, reefs, piers, and inlets. Beachgoers are encouraged to enjoy generally favorable beach conditions while remaining aware of isolated rip currents and changing weather conditions.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory from 10 AM this morning to 4 PM AST this afternoon for VIZ001-002.

AM...None.