textproduct: San Juan

KEY MESSAGES

Updated at 435 AM AST Wed May 27 2026

* Showers will affect eastern Puerto Rico and the U.S. Virgin Islands at times during the morning hours. Additional showers and isolated thunderstorms are expected this afternoon, mainly across interior and western Puerto Rico.

* Some afternoon showers could produce brief heavy rainfall. Ponding of water on roads and flooding of poor drainage areas, urban areas, and small streams will be possible, especially where showers move slowly or affect the same area more than once.

* Saharan dust will begin to filter into the region by this evening and continue through this weekend. Hazy skies and reduced visibility are possible at times, and people sensitive to dust may experience discomfort.

* Minor to moderate concentrations of Saharan dust are forecast to arrive by this evening and persist into at least this weekend, resulting in hazy skies and possible reductions in air quality and visibility, especially for sensitive groups.

Short Term(Today through Friday)

Issued at 435 AM AST Wed May 27 2026

During the overnight hours, Doppler radar detected shower development over the regional waters. However, most of this activity remained offshore, with only brief showers brushing localized windward coastal areas and producing minimal rainfall accumulations.

The latest model guidance continues to indicate above-normal moisture across the local area today through Thursday, with precipitable water values generally between 1.8 and 2.1 inches, followed by a slight drying trend late Thursday night into Friday. Meanwhile, mid- to upper-level troughiness will maintain colder-than- normal temperatures aloft, with 500 mb temperatures near -8 to -9 degrees Celsius and steeper 700-500 mb lapse rates. For today, trade wind flow and low-level moisture advection will support passing showers across eastern Puerto Rico and the U.S. Virgin Islands during the morning hours. Later in the day, diurnal heating, local effects, sea breeze convergence, and enhanced instability aloft will favor showers and isolated thunderstorms across the interior and western sections of Puerto Rico.

Steering winds have decreased substantially compared to earlier in the week, which could allow for somewhat higher rainfall accumulations with the strongest activity. Therefore, brief periods of moderate to locally heavy rainfall may support a limited to elevated flood risk, mainly for urban and small stream flooding, especially across poor drainage areas and locations that receive repeated shower activity. Suspended Saharan dust is expected to begin filtering into the region tonight, resulting in hazy skies and gradually reduced visibilities.

On Thursday, troughiness and above-normal moisture will persist despite the gradual arrival of Saharan dust. Although the dust may somewhat limit shower coverage and hinder rainfall development, trade wind showers are still expected across windward areas during the morning, followed by afternoon showers and isolated thunderstorms over the interior and western Puerto Rico. The presence of Saharan dust, combined with steeper mid-level lapse rates and colder temperatures aloft, could also enhance lightning development with the strongest convection. The flood risk should remain limited to elevated where locally heavy showers develop over urbanized areas and small streams.

By Friday, a more stable and drier pattern is expected as the subsidence side of the upper-level trough moves over the local area. Model guidance suggests 500-300 mb relative humidity values will plummet below 20 percent, well below normal. This drying aloft, combined with increasing Saharan dust concentrations, should limit shower and thunderstorm activity. However, southeasterly low-level winds, Saharan dust, and near- to above-normal 925 mb temperatures will favor warmer-than-normal surface temperatures, especially across northern and coastal Puerto Rico and urban areas. Therefore, an elevated heat risk is likely on Friday, and a Heat Advisory cannot be ruled out if confidence increases in heat indices reaching advisory criteria.

Long Term(Saturday through Wednesday)

Issued at 435 AM AST Wed May 27 2026

During the long-term forecast period, broad surface high pressure over the central Atlantic will remain the dominant weather feature. This pattern will maintain a southeasterly wind flow of around 10 to 15 mph through the weekend, with winds becoming breezier early next week as speeds increase to 15 to 25 mph from Monday through Wednesday. Through the weekend, PWAT values are expected to remain near normal, generally ranging between 1.5 and 1.75 inches. Although a more stable pattern is anticipated overall, local effects and diurnal heating will continue to promote afternoon convection, mainly across northwestern Puerto Rico. The strongest activity could produce periods of moderate to locally heavy rainfall, isolated lightning strikes, and gusty winds. This may result in a limited flood risk, including ponding of water on roads and in poorly drained areas. In addition, moderate concentrations of Saharan dust will persist across the islands, resulting in hazy skies and reduced air quality.

Early next week, global models continue to indicate a significant drying trend across the northeastern Caribbean as another surge of Saharan air spreads across the region. PWAT values are forecast to fall below normal, dropping below 1.50 inches. Based on current guidance, Monday and Tuesday appear to be the driest days of the long-term period. Furthermore, the NASA Goddard Earth Observing System model suggests moderate to high dust concentrations across the area. This pattern will promote drier and more stable conditions, limiting rainfall and thunderstorm development across Puerto Rico. Any shower activity that develops will likely remain brief and mainly confined to western Puerto Rico due to local effects.

Another primary hazard during the long-term period will be above- normal temperatures. The 925 mb temperature guidance continues to suggest temperatures in the 75th percentile. Limited cloud cover, persistent hazy skies, and southerly winds will continue to support a warming trend across the region. As a result, elevated heat indices are expected through at least Tuesday, and the issuance of Heat Advisories cannot be ruled out. Residents and visitors should take precautions to avoid heat-related illnesses, including staying hydrated and limiting prolonged sun exposure during the hottest hours of the day.

AVIATION

(06Z TAFS) Issued at 435 AM AST Wed May 27 2026

VFR conds expected to prevail at all terminals. VCSH/-SHRA psbl at TJSJ/TIST/TISX thru mrng hrs with no sig VIS reductions. Aftn SHRA/TSRA expected ovr PR, with VCTS at TJBQ/TJPS and mtn obsc psbl across interior/W PR. Brief MVFR conds psbl in/near strongest SHRA/TSRA, mainly at TJBQ/TJPS btwn 27/17-22Z. E-ESE winds incr aft 27/14Z at 14-18 kt with gusts 20-25 kt, strongest at TJBQ/TJPS and USVI terminals. Winds bcmg lgt to mdt aft 27/23Z.

MARINE

Issued at 435 AM AST Wed May 27 2026

Seas are expected to continue to subside from 6 feet to around 5 feet or lower from now onwards as easterly winds gradually diminish. Regardless, choppy seas are posible in some areas over the offshore Atlantic waters as a high pressure system remains over the central Atlantic maintaining a tight pressure gradient across the northeastern Caribbean. Mariners should also remain alert for afternoon thunderstorms developing near the western coastal waters of Puerto Rico, which may produce locally higher winds, rough seas, and dangerous lightning. Low concentrations of saharan dust will result in hazy skies and a slight reduction in visibility from tonight through this weekend.

BEACH FORECAST

Issued at 435 AM AST Wed May 27 2026

For today, the rip current risk is expected to gradually decrease as winds subside. However, a moderate risk of rip currents will likely continue along many northern and eastern exposed beaches through the latter part of the week. Looking ahead to next weekend, forecast guidance suggests strengthening winds could once again increase and expand the rip current risk across local beaches. In addition, afternoon thunderstorms are expected to develop each day across western Puerto Rico and may produce dangerous cloud-to-ground lightning. If thunder is heard, move indoors immediately and remain sheltered until the storm passes.

SJU WATCHES/WARNINGS/ADVISORIES

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