textproduct: San Juan

KEY MESSAGES

Issued at 235 PM AST Wed Aug 5 2026

- Hot and hazardous conditions will remain the primary weather concern through the remainder of the week and into the weekend. Heat Advisories continue through 5 PM AST this afternoon across Puerto Rico and the U.S. Virgin Islands, and additional heat products will likely be needed in the coming days as above- normal temperatures and dangerous heat indices persist.

- Passing showers and isolated thunderstorms will continue this afternoon, mainly across the interior and northwestern sections of Puerto Rico.

- A more stable air mass will settle over the region tomorrow into the weekend, bringing fewer showers and increasing concentrations of Saharan dust.

- Elevated fire weather conditions may develop tomorrow into the weekend. Lower relative humidity, drying fuels, and breezy east to east-southeast winds could increase the potential for rapid wildfire spread, particularly across areas with dry vegetation. Residents should avoid outdoor burning and exercise caution with activities that could produce sparks.

Short Term(This evening through Friday)

Issued at 235 PM AST Wed Aug 5 2026

Variable conditions persisted in the morning hours as a surface trough moved north of the CWA, bringing isolated to scattered showers and thunderstorms across the regional waters. Although isolated showers moved across portions of eastern Puerto Rico and the U.S. Virgin Islands, the WSR-88D rainfall estimation remained low. Minimum temperatures were slightly cooler than yesterday, with ASOS/AWOS stations reporting mid to upper 70s (so far, maximum temperature at the LMM airport is 92 degrees Fahrenheit), as well as stations across the islands' coastal areas. Meanwhile, higher elevations remained in the low to mid 60s. Temperatures continued to increase during the morning hours, reaching the upper 80s and low 90s across urban and low-lying areas, with heat indices exceeding 100 degrees Fahrenheit. The Heat Advisory remains in effect through 5 PM AST. The 12z RAOB reflected a more skinny profile in the low to mid levels, with PWAT values reaching 2 inches (yesterday: 1.76 inches. This change is reflected in the mid-levels, with less presence of Saharan Dust and the proximity of a surface trough, located north of the CWA. At around 15z, convection activity began for portions of interior and northwestern Puerto Rico, including local streamers. Based on the latest HIRES models, showers and isolated thunderstorms should continue in the afternoon, with the best chance of flooding over portions of northwestern Puerto Rico. Rainfall accumulations could lead to ponding of water over roadways and poorly drained areas.

The short-term forecast remains on track. Wind pattern will mostly prevail from the E-SE, becoming from the E-NE by Friday as a surface high pressure builds over the western Atlantic. The latest satellite- derived images show an area of drier and more stable airmass filtering into the region. From the latest model guidance, PWAT values should gradually drop to below climatological normal (1.2 - 1.4 inches), as low to mid level moisture content plummets as well (700 - 500 mb RH below 30 - 40 %). Additionally, an upper-level low over the Hispaniola moves westward, the influence of a mid level ridge should warm mid-level temperatures (between -5 and -6 degrees Celsius), bringing subsidence and promoting stability aloft. Hence, shower activity should become less frequent, with the most likely scenario being few isolated showers moving tonight into the morning hours over windward sections, followed by afternoon convection. The combination of daytime heating, local effects, and sea breeze convergence should favor convection activity over interior and northwestern Puerto Rico, though rainfall accumulations will likely remain localized, with a low flood threat. A similar pattern could repeat on Friday, with showers becoming more progressive as the surface high pressure and winds strengthen. Nevertheless, no flood nor lightning threat is expected.

As mentioned in the previous discussion, heat remains as the main threat in the short-term, as warmer to hot conditions will likely continue according to model guidance. Combined with the available moisture, heat indices will easily exceed 100 degrees Fahrenheit, particularly over urban and lower elevations of the islands. Hence, h eat products will likely be issued, without ruling out an Extreme Heat Warning.

Long Term(Saturday through Wednesday)

Issued at 142 AM AST Wed Aug 5 2026

A drying trend is expected for most of the long-term period as a strengthening, broad surface high-pressure system extending across the western and central Atlantic dominates local weather conditions. Under this pattern, an east-to-southeast wind flow will prevail through Monday, turning east-northeasterly from Tuesday onward.

An upper-level low-pressure system moving across the region from Saturday into Monday will provide slight instability aloft, reflected in cooler 500 mb temperatures dropping to between -6C and -7C. However, despite this atmospheric setup, overall drier conditions are expected, though patches of low-level moisture carried by the trade winds will move across the region from time to time. During this period passing showers will affect eastern Puerto Rico and the U.S. Virgin Islands during the morning hours. Followed in the afternoon, available moisture combined with diurnal heating and local sea-breeze effects could trigger localized convective activity across central and western Puerto Rico.

Warmer-than-normal temperatures will persist throughout the forecast period. Model guidance indicates 925 mb temperatures near two standard deviations above normal for this time of year, which, combined with lingering moisture, could result in Heat Advisories or Extreme Heat Warnings, particularly on Monday.

AVIATION

(18Z TAFS) Issued at 235 PM AST Wed Aug 5 2026

Mainly VFR conds should persist across TAF sites, with TEMPO over JBQ as CIGs/VIS may drop and lead to MVFR conds due to -TSRA in NW PR through at least 05/20z, while VCSH may persist across most terminals aft 05/23z. Winds from the E-SE may weaken and become VRB tonight, strengthening btwn 10 - 15 kt with brf gusts aft 06/12-13z. VCTS is expected once again at JBQ by 06/17z.

MARINE

Issued at 235 PM AST Wed Aug 5 2026

Marine conditions remain generally favorable across the regional waters tonight, with seas of 2 to 4 feet and east to east- southeasterly winds of 10 to 15 knots. Isolated thunderstorms over western Puerto Rico may produce locally higher winds, rough seas, and frequent lightning through the late afternoon. A strengthening surface high over the western Atlantic will promote increasing easterly winds from Thursday into the weekend, resulting in choppier seas, particularly across the offshore Atlantic waters and local passages. Moderate concentrations of Saharan dust are expected to return late Friday and persist through the weekend, reducing visibility at times.

BEACH FORECAST

Issued at 235 PM AST Wed Aug 5 2026

A low risk of life-threatening rip currents will continue tonight for most local beaches. As easterly winds strengthen late Thursday, a moderate risk of rip currents is expected to develop along the north- and east-facing beaches of Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands, continuing into the weekend.

Heat remains the primary beach hazard through the remainder of the week and into the weekend, with above-normal temperatures and elevated heat indices expected each day. Beachgoers are encouraged to stay hydrated, seek shade frequently, and limit prolonged sun exposure during the afternoon hours. Isolated thunderstorms this afternoon may produce locally hazardous conditions across the northwestern coastal waters and beaches of Puerto Rico before a more stable weather pattern develops for the latter part of the week. Moderate Saharan dust concentrations are expected to return late Friday into the weekend, occasionally reducing visibility.

FIRE WEATHER

Issued at 235 PM AST Wed Aug 5 2026

Critically dry fuels continue across portions of the local islands, particularly across southern Puerto Rico, St. Croix, and other fire- prone areas of the U.S. Virgin Islands. Although isolated showers and localized thunderstorms remain possible this afternoon, mainly across interior and western Puerto Rico, recent rainfall has been limited over the southern coastal plains, where fuels remain receptive to fire starts. Winds will remain relatively light today, keeping the fire weather threat limited through the remainder of the afternoon.

A drier and more stable weather pattern will become established beginning Thursday and persist into the weekend as moisture decreases and easterly winds strengthen. Lower relative humidity, increasing sunshine, and breezy conditions, combined with critically dry fuels, will elevate the potential for rapid wildfire growth and spread, particularly across southern Puerto Rico and the U.S. Virgin Islands. Residents and visitors are encouraged to avoid outdoor burning and use caution with activities that could produce sparks, as fire weather conditions are expected to become increasingly favorable in the coming days.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory until 5 PM AST this afternoon for PRZ001>005-007- 008-010>013.

VI...Heat Advisory until 5 PM AST this afternoon for VIZ001-002.

AM...None.