textproduct: San Juan

KEY MESSAGES

Issued at 442 AM AST Sat Jul 18 2026

* Hot conditions will continue through next week. Elevated heat indices are expected across urban and coastal areas each afternoon, with localized areas briefly reaching Heat Advisory thresholds during the weekend.

* A few passing showers and isolated afternoon showers over western Puerto Rico are expected each day. Little to no flooding impact is expected.

* Breezy conditions will persist through the weekend.

* Another pulse of moderate Saharan dust will spread across the islands Sunday into Monday, resulting in hazy skies, reduced air quality, and a potentially higher heat risk due to warmer overnight temperatures.

Short Term(Today through Monday)

Issued at 442 AM AST Sat Jul 18 2026

Fairly tranquil weather conditions prevailed overnight across Puerto Rico and the U.S. Virgin Islands. A generally stable weather pattern will persist across the region through the short-term period. Latest satellite-derived TPW imagery and model guidance continue to indicate below-normal moisture across the northeastern Caribbean, with precipitable water values generally ranging between 1.3 and 1.5 inches today. A weak tropical wave is forecast to approach the local islands on Sunday afternoon into Monday; however, the associated moisture remains limited and is expected to interact with a persistent dry mid-level air mass and an increasing Saharan Air Layer (SAL), resulting in little change to the overall weather pattern.

Mid-level ridging will remain established over the northeastern Caribbean through the weekend, maintaining warm temperatures aloft and below-normal relative humidity between 700 and 500 mb. Forecast soundings continue to indicate a relatively stable atmosphere characterized by weak lapse rates, limited instability, and very dry mid-level air. As a result, shower activity will remain mostly shallow despite a slight increase in low-level moisture accompanying the tropical wave. Passing trade wind showers will continue to affect the windward sectors from time to time, while afternoon convection will once again be confined to portions of western Puerto Rico each day due to local effects and daytime heating. The increasingly stable environment should limit the coverage and intensity of convection, with any heavier showers expected to be brief and localized. Consequently, little to no flooding impacts are expected.

A tight surface pressure gradient will continue to promote breezy to locally windy conditions through the period, particularly across coastal areas and higher elevations. By Sunday night into Monday, another pulse of moderate Saharan dust is expected to overspread the region behind the tropical wave, leading to hazy skies, reduced visibilities at times, and deteriorating air quality, especially for sensitive groups.

Afternoon temperatures will continue to reach the upper 80s to low 90s across the urban and coastal areas. While the overall heat threat is expected to remain limited, localized areas may briefly reach Heat Advisory criteria during the peak afternoon hours today and Sunday. On Monday, the arrival of the Saharan Air Layer may inhibit overnight cooling, resulting in warmer minimum temperatures and potentially increasing the heat risk across portions of the coastal and urban areas. Although Heat Advisory conditions may become more widespread on Monday, confidence remains somewhat limited, and forecast trends will continue to be monitored.

Overall, little change is expected through the short-term period, with breezy, hot, and relatively stable conditions prevailing across the islands. The primary weather impact will remain the heat, with localized Heat Advisory conditions possible each afternoon across the urban and coastal areas. Otherwise, passing trade wind showers and isolated afternoon convection over western Puerto Rico will result in limited impacts, while another pulse of Saharan dust arriving Sunday into Monday will lead to hazy skies, deteriorating air quality, and may contribute to an increased heat risk early next week.

Long Term(Tuesday through Saturday)

Issued at 442 AM AST Sat Jul 18 2026

By Tuesday, Saharan dust concentrations are expected to decrease to low levels. At the same time, the latest guidance suggests that environmental conditions will become more favorable for convective activity due to the influence of a series of upper-level lows and troughs. Winds will become lighter from the east-northeast. At 500 mb, temperatures are forecast to cool from above-normal values to near seasonal levels, around -6C to -7C. In addition, lower 250 mb heights, near-seasonal mid-level relative humidity, and precipitable water values increasing to around 1.7 to 1.9 inches will support a more favorable environment for shower and thunderstorm development.

As a result, Tuesday is expected to have the highest rain chances of the long-term forecast period, particularly during the afternoon hours. A limited flood risk is highlighted across west-central and western Puerto Rico due to the potential for ponding of water on roads and in poorly drained areas, along with a low chance of urban and small-stream flooding.

By Wednesday, afternoon convection is also expected to develop across the northwestern quadrant of Puerto Rico as winds gradually veer to a more southeasterly direction. Another primary concern for Tuesday and Wednesday will be the heat risk. With the increase in available moisture, conditions are expected to become and feel warmer. An elevated heat risk is forecast for Tuesday. By Wednesday, the combination of light southeasterly flow, seasonal moisture, and 925 mb temperatures around two standard deviations above normal is expected to result in the warmest day of the week, with probably elevated or significant heat risk. High temperatures are forecast to reach the lower to middle 90s across coastal and urban areas during the early afternoon hours. Heat index values will likely reach hazardous levels each afternoon, especially across urban and coastal locations. Heat products will likely be needed on both days. Residents and visitors are encouraged to continue practicing heat safety measures to reduce the risk of heat-related illnesses.

Drier air is expected to filter into the region on Thursday, with PWAT values briefly decreasing into below normal values, resulting in more limited shower activity. Winds are forecast to strengthen once again, becoming breezy to locally windy through the weekend. From Friday into Saturday, the steering flow will continue to favor passing showers across windward areas during the nighttime and morning hours, followed by afternoon showers over western Puerto Rico driven by local effects and seasonal precipitable water values. A limited heat risk is expected to persist through the end of the week.

AVIATION

(06Z TAFS) Issued at 442 AM AST Sat Jul 18 2026

VFR conds will prevail at all TAF sites through the fcst pd. Brief aftn SHRA developing over the interior and W PR, but only minor operational impacts are expected. E-ESE winds will increase aft 18/13Z to 15-20 kt with gusts up to 30 kt, producing sfc wind variations due to sea breeze influences. Winds diminish aft 18/23Z, becoming 10 kt or less overnight.

MARINE

Issued at 442 AM AST Sat Jul 18 2026

A surface high over the central Atlantic will maintain moderate to locally fresh east winds and hazardous conditions for small craft through the weekend. Gusts up to 30 knots are expected, with seas generally between 3 and 6 feet, occasionally reaching 8 feet across portions of the Caribbean waters and Mona Passage this weekend. Saharan Dust will linger, with another plume arriving late Sunday into early next week, resulting in hazy skies and locally reduced visibility.

BEACH FORECAST

Issued at 442 AM AST Sat Jul 18 2026

A moderate risk of rip currents will spread across more beaches of Puerto Rico and the U.S. Virgin Islands today as enhanced easterly winds generate increasingly choppy, wind-driven seas. Life- threatening rip currents will remain possible through Monday, with the risk decreasing to low Tuesday and Wednesday as winds and seas subside.

Breezy conditions and choppy seas will remain a concern for beachgoers through Monday, with the strongest winds expected Sunday. Looking ahead, heat-related risks are expected to increase Tuesday and peak Wednesday, particularly for those spending extended periods outdoors. Saharan Dust will linger through the weekend, with another plume arriving late Sunday into early next week, resulting in hazy skies and locally reduced visibility.

FIRE WEATHER

Issued at 442 AM AST Sat Jul 18 2026

Elevated fire weather conditions will persist today across portions of Puerto Rico, particularly along the southern coastal plains and adjacent lower elevations. Relative humidity values are expected to fall into the upper 40s to lower 50s this afternoon, while breezy easterly winds of 15 to 20 mph, with higher gusts, will continue to support favorable conditions for rapid fire spread.

Critically dry fuels remain in place, with KBDI values exceeding 700 across much of Puerto Rico. Although isolated afternoon showers may develop over western Puerto Rico, rainfall coverage and amounts will be insufficient to provide meaningful relief to the ongoing dry conditions. Therefore, elevated fire weather conditions will continue today, where a Fire Danger Statement remains in effect.

SJU WATCHES/WARNINGS/ADVISORIES

PR...None. VI...None. AM...None.