textproduct: San Juan

KEY MESSAGES

Issued at 254 PM AST Tue Jul 28 2026

- A Heat Advisory remains in effect through 5 PM AST for coastal and urban areas of Puerto Rico and the U.S. Virgin Islands, where dangerous heat indices are expected. High heat indices are expected to continue each late morning to afternoon during the next several days.

- Showers and t-storms are forecast to continue developing this afternoon under east-southeast flow. In the meantime generally moderate concentrations of Saharan Dust will continue moving westward over the region.

- A drier air mass, accompanied by additional Saharan dust, will move over the region tomorrow afternoon onwards through the end of the week, reducing rainfall coverage while maintaining hot and hazy conditions and increasing the fire weather risk.

- Increasing winds will promote up to a moderate risk of life- threatening rip currents along the beaches of Puerto Rico and the U.S. Virgin Islands through the rest of the week.

- Another tropical wave may approach the region late this weekend. While it could increase the potential for showers and thunderstorms, confidence in the timing and impacts remains low at this time.

Short Term(This evening through Thursday)

Issued at 254 PM AST Tue Jul 28 2026

Mainly fair weather conditions have prevailed across the forecast area throughout the morning hours. An elevated heat risk has persisted due to the combination of hot temperatures and high humidity, allowing heat indices across urban and coastal areas of the islands to reach levels that can affect most individuals sensitive to heat. Take the necessary precautions, particularly if spending prolonged periods of time outdoors during the peak heating hours. As a note, a record high temperature of 93F was set today at the San Juan Area, specifically at the Luis Munoz Marin International Airport climate station. This breaks the previous record of 92F set in 1981. Winds have generally ranged between 10 and 15 mph, with occasional higher gusts.

For the rest of the afternoon, convective activity driven by daytime heating, sea-breeze convergence, and orographic effects is expected to develop across the north-central and west-central to northwestern municipalities of Puerto Rico. This will result in a limited to elevated flood risk, with the potential for ponding of water on roads and localized flooding in urban areas, roads, and in small streams.

Tonight into Wednesday, as the Atlantic high-pressure system continues to strengthen, the pressure gradient will tighten, bringing breezy to windy conditions, with the strongest winds expected between Wednesday and Thursday. In addition, the trailing moisture associated with the tropical wave will gradually shift west of the area as a drier air mass, accompanied by low to moderate concentrations of Saharan dust, spreads across the region. These particulates are expected to remain present through the rest of the forecast period. Nevertheless, available low-level moisture and daytime heating will continue to support afternoon showers and isolated thunderstorms, mainly across the northwestern quadrant of Puerto Rico. The flood risk will remain limited. By Thursday, the latest model guidance remains consistent, indicating that precipitable water values will remain below 1.5 inches, which is below the climatological normal (around the 25th percentile). As a result, the potential for widespread convection will be lower.

For the remainder of the short-term forecast period, although drier air will continue to spread across the region, warm to hot conditions will persist across coastal and urban areas, as reflected by above-normal 925-mb temperatures. Residents and visitors are encouraged to stay hydrated and take the necessary precautions to minimize heat-related impacts.

..Long Term(Friday through Tuesday)

Issued at 339 AM AST Tue Jul 28 2026

A variable weather pattern may be expected in the long-term forecast. A surface high pressure over the Central Atlantic will dominate most of the wind pattern, mainly from the ESE-SE through most of the period, though it may become from the northeast by late Monday night. Although conditions will remain breezy during the upcoming weekend, winds may weaken by the end of the period.

Based on the latest model guidance, patches of moisture may arrive by Friday morning, with isolated showers moving across the regional waters and windward sections of the islands, followed by afternoon convection over portions of northwestern Puerto Rico. Although the latest model solution suggests an increase in low- and mid-level moisture, lingering Saharan dust concentrations and strong winds may not lead to significant flooding or lightning threat. A similar weather pattern may repeat on Saturday, though a drier slot may move across the CWA by the afternoon along with ridging in the mid-levels that should limit shower activity and lower flooding risk.

The weather pattern on Sunday and Monday may become slightly unstable as a tropical wave and an upper-level low approach the local area, introducing tropical moisture and instability across the CWA. The latest global model solutions suggest an increase in both low- to mid-level moisture (above 60 - 70%), cool mid-level temperatures (500 mb temperatures between -6 and -7 degrees Celsius), and enhanced lifting promoting cloud growth and introducing instability, though they differ with timing. While the latest deterministic guidance of the GFS suggests the bulk of moisture arriving on Sunday afternoon into the evening, the ECMWF delays the tropical wave until Monday morning. Although both models position the upper-level low over Hispaniola early Monday and suggest an increase in shower and thunderstorm activity, this introduces uncertainty to the forecast. Another factor that introduces uncertainty to the forecast is another plume of Saharan dust accompanying the tropical wave, which may weaken it by the time it moves across the area. Hence, the flooding threat will remain limited for both days, particularly over western/northwestern Puerto Rico due to the combination of available moisture, daytime heating, and local effects.

Under an ESE-SE wind flow, warmer to hotter temperatures can be expected across the CWA, particularly over urban and low-lying areas. With the available moisture content, heat indices will likely exceed 100 degrees Fahrenheit and affect most individuals, particularly those without adequate hydration or effective cooling. Therefore, the heat threat will remain elevated throughout the forecast period; Heat Advisories may be issued if required.

AVIATION

(18Z TAFS) Issued at 254 PM AST Tue Jul 28 2026

Mainly VFR conditions across most TAF sites during this forecast period. Except in TJBQ where VCTS/TSRA will remain more probable from 28/18-21Z. This will likely result in intermittent MVFR conds. Low to moderate concentrations of Saharan dust spreading across the region will result in slightly VIS reductions from this afternoon into the coming days. Another aviation concern will be the winds which are expected to increase, with gusts near 30kts after 29/13- 14Z through 29/23Z.

MARINE

Issued at 254 PM AST Tue Jul 28 2026

Moisture associated with a tropical wave will start to depart the local waters tomorrow afternoon, as drier air with Saharan Dust takes its place. East to east-southeast flow will become more moderate to fresh by later this afternoon into Wednesday as a high pressure system continues to strengthen over the Atlantic, tightening the pressure gradient. These winds will maintain choppy seas across portions of the Atlantic waters, offshore Caribbean waters, and the local passages, with seas up to 6 feet expected in localized areas, through the weekend.

BEACH FORECAST

Issued at 254 PM AST Tue Jul 28 2026

Up to a moderate risk of rip currents (life-threatening rip currents are possible in the surf zone) is forecast across northern Puerto Rico tonight. A low risk of rip currents is expected to continue elsewhere, however, life-threatening rip currents often occur in the vicinity of groins, jetties, reefs, and piers. High pressure over the Atlantic will strengthen, causing winds to continue increasing this afternoon and maintaining breezy to locally windy conditions through the remainder of the week. Consequently, a moderate risk of rip currents will affect most beaches across Puerto Rico and the U.S. Virgin Islands. Furthermore, coastal and low-elevation sectors will experience prevailing warm to hot conditions. It is advised to stay hydrated and take regular breaks in shaded areas.

FIRE WEATHER

Issued at 254 PM AST Tue Jul 28 2026

Surface station have been reporting minimum relative humidity values near or above critical thresholds today, critically dry fuels persist across southern Puerto Rico and St. Croix. Easterly winds are forecast to become breezy to windy, particularly Wednesday and Thursday, which could promote the spread of any fire that develops. Additionally, a drier airmass accompanied by Saharan dust will spread over the region. Residents and visitors should avoid outdoor burning and exercise caution with activities that could generate sparks or open flames. Fire weather partners should continue to monitor the forecast.

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.