textproduct: San Juan

KEY MESSAGES

Issued at 321 AM AST Sat Aug 29 2026

- Heat remains a concern today. A Heat Advisory is in effect today from 10 AM to 5 PM AST. A brief relief is expected Sunday into Monday before hazardous heat returns around midweek.

- More unsettled and windier conditions are expected Sunday into Monday as moisture associated with Dolly's remnants moves across the region. Lingering moisture may continue into Tuesday.

- The main hazards will be urban flooding, lightning, and gusty winds, especially Sunday into Monday. The potential for isolated flash flooding is lower but cannot be ruled out. Rainfall amounts and the location of the highest totals remain uncertain.

- Marine and coastal conditions will become hazardous Sunday into Monday as winds and seas build. Small Craft Advisory is in effect for the offshore Atlantic waters and Anegada Passage.

Short Term(Today through Monday)

Issued at 321 AM AST Sat Aug 29 2026

The overnight period was dominated by showers and even a few thunderstorms over the local waters, and some passing showers reaching eastern portions of Puerto Rico. This activity is associated to the moisture of a weak tropical wave moving across the region, maintaining PWAT values around 2 inches as showed in satellite-derived imagery, and will remain present through at least the morning hours. Winds were mainly from the east to east- southeast at 10 mph or less and overnight generally in the upper 70s to lower 80s across coastal areas.

Today, as this moisture field continues to move rapidly west of the region, a drier airmass will filter into the area by mid- morning and persist through the rest of the day. This will limit shower activity, with only localized showers expected during the afternoon across western Puerto Rico, driven primarily by local effects. Overall, the flooding risk is expected to be none to low. The primary concern today will be the heat. The combination of available moisture, above-normal minimum temperatures, east- southeast winds, limited rainfall, and 925-mb temperatures in the 75th percentile of climatology will likely result in another day of hot temperatures and elevated heat indices. Therefore, a Heat Advisory is in effect today from 10 AM to 5 PM AST across coastal and urban areas of Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands.

By late Saturday into Sunday, moisture associated with a tropical wave, the remnants of Dolly, is forecast to begin arriving in the region from the east. The latest model guidance suggests PWAT values increasing to between 2 and 2.5 inches and remaining elevated throughout the forecast period. This increase in moisture will extend into the mid and upper levels of the atmosphere as well. Therefore, particularly from Sunday into Monday, we will transition toward a more unsettled weather pattern. Shower and thunderstorm activity should first increase across the U.S. Virgin Islands as early as Sunday morning, spread into Vieques, Culebra, and eastern Puerto Rico by Sunday morning into the early afternoon, and then expand across Puerto Rico. Periods of squally weather will bring moderate to locally heavy rainfall. While this rainfall is not expected to end the ongoing drought, it could still provide beneficial rainfall. The main concerns from Sunday into Monday will be urban and poor-drainage flooding, lightning, and gusty winds. Periods of heavy rainfall will support a limited to elevated excessive rainfall risk, with urban and poor-drainage flooding becoming increasingly likely.

With increased cloud cover and rainfall, temperatures should be lower Sunday and Monday, providing a brief relief from the heat. Residents, visitors, and local officials are encouraged to continue monitoring the forecast as uncertainty decreases.

Long Term(Tuesday through Saturday)

Issued at 321 AM AST Sat Aug 29 2026

Deep tropical moisture trailing from the previous tropical wave (the remnants of Tropical Storm Dolly) will remain in place across the forecast area on Tuesday, with GFS model guidance indicating precipitable water (PWAT) values near the 75th percentile for this time of year. At the surface, a weak disturbance (previous dolly) positioned west of the region over Hispaniola will maintain a south- southeasterly wind flow across the local islands. Under this pattern, an unstable, wet weather pattern will prevail, favoring some widespread showers with isolated thunderstorms across eastern Puerto Rico, including the San Juan metro area in the morning hours followed by afternoon showers along the interior west and northwestern sections. By Wednesday, low-level winds will shift from the east-southeast as surface high pressure anchors over the western Atlantic and another extends across the Central Atlantic. This configuration will bring a more variable moisture regime as pockets of deep moisture alternate with drier air patches, resulting in hot and warm conditions with heat indices that could reach 111 degrees across coastal and urban sections. Although conditions will not be favorable for morning advective showers, localized afternoon convective development is expected over interior and western Puerto Rico.

According to the model guidance today, Thursday is forecast to be the driest day of the long-term period as a drier air mass filters into the region, suppressing, in some way, widespread cloud development and keeping maximum temperatures elevated across coastal areas. On Friday, the surface high over the Central Atlantic will extend further south, enhancing easterly trade winds that will push occasional patches of trade wind moisture across the regional waters. By late Friday into Saturday, global model guidance suggests an increase in moisture associated with another tropical wave approaching the local area. In response to the strengthening surface high pressure over the Central Atlantic, low-level winds will veer slightly to the east-southeast, pulling this deeper moisture field across the CWA. This pattern will increase the potential for organized shower and thunderstorm activity heading into the weekend, with localized urban and small-stream flooding risks returning to the forecast area.

AVIATION

(06Z TAFS) Issued at 321 AM AST Sat Aug 29 2026

Mainly VFR conditions expected throughout the forecast period. VCSH possible this morning across TJSJ, with additional VCSH developing across W PR aft 29/18Z. Showers are not expected to be as frequent over TJBQ, although brief VCSH cannot be ruled out. E to ESE winds of 15 to 20 kts are expected, with occasional higher gusts, gradually decreasing to around 10 to 12 kt overnight. The frequency of VCTS/SHRA is expected to increase across the USVI terminals after 29/23Z and into the overnight hours as increasing moisture associated with a tropical wave moves into the region.

MARINE

Issued at 321 AM AST Sat Aug 29 2026

A weak tropical wave will exit the local area today, and shower activity is expected to diminish across the regional waters during the day. However, this will be brief as the remnants of Tropical Storm Dolly, now a strong tropical wave, are expected to move across the local area from tonight through late Sunday. Squally weather, strong gusts, and hazardous seas are expected across most waters. Small craft advisory conditions are expected mainly for the Atlantic waters and the Anegada Passage on Sunday and Monday.

BEACH FORECAST

Issued at 321 AM AST Sat Aug 29 2026

There is a moderate risk of rip currents along the east and north facing beaches of Puerto Rico and the U.S. Virgin Islands today. Beachgoers must exercise caution, as life-threatening rip currents are possible along the surf zone. For Sunday and Monday, swells generated by Tropical Storm Dolly and its remnants will increase the risk to high across the same areas; inexperienced surfers and beachgoers are urged to remain out of the water due to the expected strong currents and rough surf along unprotected coastlines. In addition, thunderstorms with cloud-to-ground lightning and gusty winds are expected during this period across all islands and coastal waters.

FIRE WEATHER

Issued at 321 AM AST Sat Aug 29 2026

A drier-than-normal air mass will move into the region by midmorning today, replacing the moisture associated with a weak tropical wave. As a result, minimum relative humidity values are expected to fall into the mid-50s or lower across portions of the islands. Easterly winds of 12 to 18 mph are expected, with locally higher gusts, especially near coastal areas. These conditions, combined with dry fuels due to ongoing rainfall deficits, will increase the potential for wildfire ignition and rapid spread.

Therefore, an elevated fire danger is expected today across portions of the southern plains and hills of Puerto Rico, as well as Vieques, Culebra, and the U.S. Virgin Islands. A Fire Danger Statement is in effect from 10 AM through 5 PM AST for these areas. Fire weather partners are encouraged to continue monitoring the forecast for possible updates. Residents and visitors are strongly urged to avoid outdoor burning, as conditions will easily support wildfire ignition and rapid spread.

Increasing moisture and rain chances later tonight, continuing into Sunday and early next week, are expected to reduce the fire- weather threat.

HYDROLOGY

Issued at 321 AM AST Sat Aug 29 2026

The remnants of Tropical Storm Dolly will arrive into the area on Sunday and Monday as a strong tropical wave. A widespread and long-lasting rainfall event is not anticipated at this time. Instead, areas of squally weather will bring periods of moderate to locally heavy rainfall. These rains are expected to be mostly beneficial due to the ongoing drought, but are not expected to be enough to end the severe to extreme drought conditions. While the risk of flooding will be low to locally moderate, some areas may experience flooding if the drainage system is clogged with dead vegetation debris or if it is in an area with poor drainage. Please refer to the latest Hydrologic Outlook, ESFSJU, for more details.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 5 PM AST this afternoon for PRZ001>005-007-008-010>013.

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

AM...Small Craft Advisory from 6 AM Sunday to noon AST Monday for AMZ711.

Small Craft Advisory from 6 AM Sunday to 6 AM AST Monday for AMZ723.