textproduct: San Juan

KEY MESSAGES

Updated at 210 PM AST Tue Aug 25 2026

* An Extreme Heat Warning is in effect for portions of Puerto Rico this afternoon, with dangerously hot conditions expected. The heat threat will remain elevated throughout the period.

* A weak tropical wave will continue to promote showers and thunderstorms this afternoon, with a limited flooding risk, mainly across interior and northwestern Puerto Rico.

* Saharan dust will increase tonight into Wednesday, promoting hazy skies and reduced rainfall coverage across Puerto Rico and the US Virgin Islands.

* A tropical wave will bring deeper moisture Friday night into the weekend, with Saturday having the greatest potential for increased rainfall.

* The risk of rip currents will increase to moderate from Wednesday onward, particularly along northern and eastern- exposed beaches.

Short Term(This evening through Thursday)

Issued at 210 PM AST Tue Aug 25 2026

Mostly fair weather conditions prevailed during the morning hours, with a few showers moving across the regional waters and the eastern portions of Puerto Rico and the U.S. Virgin Islands, while the western side of the CWA remained mostly clear with minimal cloud cover. The latest satellite-derived products show a tropical wave moving into the region, with an area of high moisture content reflected over the low and mid levels. Additionally, the 12z RAOB reported abundant moisture content, with PWAT values around 1.97 inches, mainly concentrated in the low levels (RH values around 85%). Meanwhile, the sounding shows slightly drier mid levels (RH values around 63%), though BHP-ALPW products show an increase in the 700- 500 mb layer. Around 11 PM AST, local streamers began to develop and produced isolated to scattered showers across portions of the U.S. Virgin Islands and eastern Puerto Rico, including the San Juan Metro Area. Based on the latest WSR-88D rainfall estimates, accumulations ranged between 0.50 and 0.70 inches, with isolated 0.90 values, over San Juan and Guaynabo. On the other hand, showers and isolated thunderstorm over interior and northwestern Puerto Rico left up to 1.0 - 1.50 inches over Anasco and Moca. In terms of heat, temperatures increased during the morning, with stations reporting upper 80s and low 90s and heat indices exceeding 100 degrees Fahrenheit (ASOS at the LMM International Airport reporting a preliminary maximum temperature of 92 degrees Fahrenheit). Although convection activity already began, elevated to significant heat conditions continue across the CWA, with the Heat Advisory and Extreme Warning in effect until 5 PM AST.

Variable conditions will continue in the short-term forecast. The latest satellite-derived products show a slightly drier airmass along with moderate to high concentrations of Saharan Dust. Model guidance suggests PWAT values diminishing briefly to near below climatological normal (around 1.6 inches), with low and mid level moisture content dropping to 20 - 40%. Although conditions seem unfavorable for deeper convection, the combination of the available moisture, daytime heating, and local effects should enhance shower activity across interior and western/southwestern Puerto Rico. Rainfall accumulations will likely remain minimal, though isolated areas can expect ponding of water over roadways and poorly drained areas. Due to the influence of Saharan Dust, isolated thunderstorms cannot be ruled out. Followed by the afternoon convection, winds will likely shift from the E-ENE as a surface trough north of the CWA approaches the area and increases moisture content by late Wednesday night into Thursday. Looking at the latest guidance's cross-section, moisture content should increase in the low levels, with the 850 - 700 mb layer up to 70 - 80%. Although the most enhanced activity of the trough may stay north of the CWA, enough instability combined with local effects and available moisture will increase the likelihood of showers and isolated thunderstorms over windward sections of the islands during the morning, followed by afternoon convection over interior and western Puerto Rico. Although widespread flooding is not expected, rainfall accumulations could lead to minor flooding over flood-prone areas. Weather conditions should gradually improve by Thursdays evening as a drier airmass filters into the region, with limited shower activity.

Heat remains as the primary threat across the CWA, as warmer-than- normal temperatures are anticipated across the islands. Additionally, the presence of SAL will likely inhibit effective nighttime cooling and allow warmer-than-normal minimum temperatures. With the available moisture, heat indices across urban and low-lying areas of the islands can still exceed 100 degrees Fahrenheit, increasing the heat threat and affecting mainly sensitive groups without effective cooling and/or hydration. Therefore, heat products (Advisory/Warning) will likely be issued.

Long Term(Friday through next Monday)

Issued at 309 AM AST Tue Aug 25 2026

Patches of moisture with seasonal precipitable water (PWAT) values will move across the islands on Friday under a generally easterly steering flow to start the long term period, bringing in showers over windward sectors to start the morning hours. Diurnal heating, sea breeze convergence and local effects will also result in afternoon showers and t-storms over mainly western Puerto Rico. Available moisture however will be mostly limited to the lower levels. An elevated heat risk is also possible over urban and coastal sectors.

A tropical wave, and its associated moisture field, will then approach the islands Friday night and push PWAT values to above normal, above 2 inches, through at least the overnight hours Saturday into Sunday. Available moisture can also reach deeper in the atmosphere, further prompting a flooding risk. Steering flow will be generally ESE and can result in showers and possible t- storms moving over the islands during the overnight and morning hours, while afternoon showers and t-storms are forecast to develop over interior to W-NW PR as well as downwind of the local islands and El Yunque. This period is forecast to be the most humid and the most likely to feature increased rain chances.

Drier air is then forecast to move over the area on Sunday, resulting in below normal PWAT values and, according to the latest guidance, more moderate Saharan Dust concentrations moving over the area as available moisture is once again confined to the lower levels. Afternoon convection is still forecast over W to NW under ESE steering flow. Uncertainty increases to start the next workweek due to the tropical wave AL96 currently over the eastern tropical atlantic (please see the latest Tropical Weather Outlook for the most up to date information regarding this wave). The current forecast is based on generally easterly steering flow veering to become more south-southeasterly and steering patches of moisture and drier air over the islands, with showers moving over windward sectors and afternoon convection develops. Given forecast uncertainties, residents and local interests are advised to track upcoming updates as AL96 moves over the Atlantic. Seasonal to above seasonal 925 mb temperatures will persist during the period and result in elevated to possibly significant heat risks each day, with the highest chances of a more limited heat risk being on Saturday.

AVIATION

(18Z TAFS) Issued at 210 PM AST Tue Aug 25 2026

Mainly VFR conds will prevail across all terminals, though aftn convtn producing -TSRA will likely reduce CIGs/VIS across JBQ, leading to brf MVFR conds btwn 25/18-20z. Meanwhile, VCTS should continue across JPS while JSJ, IST, and ISX can expc mainly typical VCSH through 25/22-23z, with SAL concentrations leading to HZ and reducing VIS. Winds from the E-ESE should weaken and become VRB btwn 5 - 10 kts by 25/23z, strengthening once again btwn 12 - 15 kts and gusts up to 25 kts.

MARINE

Issued at 210 PM AST Tue Aug 25 2026

Surface high pressure extending across the western and central Atlantic will continue to support moderate east to east- southeasterly winds across the regional waters, becoming locally fresh at times. Increasing moisture associated with a tropical wave will promote additional shower and thunderstorm development across the western local waters and Mona Passage into tonight. Locally higher winds, choppy seas, and reduced visibility can be expected in and around thunderstorms. Saharan dust concentrations will increase tonight and peak on Wednesday, resulting in hazy skies and slightly reduced visibility. A weak long-period northerly swell remains forecast to arrive and spread across the regional waters by Thursday.

BEACH FORECAST

Issued at 210 PM AST Tue Aug 25 2026

A low risk of rip currents will continue through at least tonight across the local islands. Nonetheless, beachgoers should exercise caution, as life-threatening rip currents can still occur near jetties, reefs, groins, and piers.

By Wednesday, a gradual increase in winds and seas will likely result in a moderate risk of rip currents, particularly along the northern and eastern-exposed beaches of the islands. The moderate risk is expected to continue through the end of the week.

Increasing moisture associated with a tropical wave will support showers and isolated thunderstorms across the regional waters and coastal areas this afternoon, mostly across northwestern portions of Puerto Rico. Beachgoers should remain weather alert, as thunderstorms could produce gusty winds and dangerous lightning.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Extreme Heat Warning until 5 PM AST this afternoon for PRZ001>005-007-008-010-011.

Heat Advisory until 5 PM AST this afternoon for PRZ012-013.

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

AM...None.