textproduct: San Juan

KEY MESSAGES

Updated at 301 PM AST Thu Jun 4 2026

* Hot temperatures are expected each afternoon, with heat indices above 100 degrees for many urban and coastal area, as well as the valleys of the interior. This level of heat affects mos individuals sensitive to heat, especially when outdoors without effective cooling or adequate hydration.

* Small concentrations of Saharan dust will persist through Saturday, but concentrations will increase on Sunday. Those sensitive to this particulate should exercise caution if planning to spend long period of times outside.

* A moderate rip current risk will persist for most beaches of eastern and northern Puerto Rico, Vieques, Culebra and the Virgin Islands through at least the middle of next week.

* For the Virgin Islands, after a mostly cloudy morning, skies cleared out for the afternoon. Mostly fair weather, with hot temperatures and a little dust will persist through the weekend.

Short Term(This evening through Saturday)

Issued at 301 PM AST Thu Jun 4 2026

A shallow patch of moisture moving over the region has prompted an increase in cloudiness and fast-moving shower activity. Steered by ESE flow, this patch of moisture has reached around (satellite derived) 1.50 in of precipitable water (PWAT), below normal values for this time of the year. A surface high pressure over the central to eastern Atlantic, as well as a frontal low moving northwards in the western Atlantic will result in ESE to SE steering flow during the rest of the workweek. PWAT and low level relative humidity values will fluctuate throughout the period with PWAT values staying below normal to low end normal values through tomorrow before dipping to around 1.35 in tomorrow morning and then gradually increasing and reaching normal values (around 1.75 in) on Saturday. Low level RH will follow a similar pattern with a notable dip towards below normal values tomorrow morning, as drier air filters in, before a gradual increase to more normal values. The increase in moisture late in the period will be due to the moisture field of a tropical wave that will be well southeast of the region to end the period. This available moisture will be shallow however, with drier air above 800 mb towards the mid levels and generally stable conditions in the upper levels. Current satellite imagery as well as NASA/GMAO dust aerosol optical thickness model guidance indicates that a plume of low to locally moderate Saharan Dust concentrations will continue to filter over the region during the rest of the workweek. More generally moderate concentrations should arrive late Friday and into the long term period. This Saharan Air Layer (SAL) will result in hazy skies, reduced visibility and deteriorated air quality. Available diurnal heating, sea breeze convergence and prominent steering flow have resulted in the formation of showers over interior to northern PR, particularly over NW PR while the above mentioned patch of moisture has aided in the formation of showers over the eastern region throughout the day. Passing showers will continue to reach windward areas during the period, although inhibited, shallow, and with low accumulations due to the approaching drier air while afternoon convection is also forecast in similar areas as today under the up to breezy ESE to SE steering flow. This pattern will have additional moisture on Saturday as PWAT values gradually increase. Warm to hot conditions will continue throughout the period, although somewhat inhibited today due to the increase in cloudiness (remaining in a limited heat risk). Heat indices are still forecast to reach above 100 to 105F each afternoon during the short term period at urban and low elevation areas, reaching up to an elevated heat risk. Sensitive groups to hazy and/or hot conditions should take their precautions.

LONG TERM(Sunday through Thursday)

Issued at 225 AM AST Thu Jun 4 2026

During the long-term period, surface high pressure over the eastern Atlantic will maintain an easterly to east-southeasterly wind flow across the local islands. Breezy winds are expected on Sunday and Monday, generally ranging between 15 and 20 mph and higher gusts, particularly along coastal areas and low-elevation areas. Thereafter, the pressure gradient is forecast to gradually weaken, resulting in lighter winds through the middle and latter part of the workweek.

Saharan dust concentrations are expected to increase from moderate to high levels on Sunday and persist through at least early next week. As a result, hazy skies, reduced visibilities, and periods of degraded air quality can be expected across the region. However, the latest model guidance continues to indicate that Sunday will likely be the wettest day of the long-term period. Moisture associated with a tropical wave is forecast to move across or near the region, with precipitable water (PWAT) values increasing to between 1.70 and nearly 2.0 inches. This surge in moisture, combined with daytime heating and local effects, will support numerous passing showers across windward sectors during the morning hours, followed by scattered to numerous showers and isolated thunderstorms across portions of western Puerto Rico during the afternoon. Although widespread flooding is not anticipated, the rainfall activity may lead to ponding of water on roadways, minor urban flooding, and localized flooding in poorly drained areas. It remains uncertain how the Saharan dust layer will interact with the moisture associated with the tropical wave, and this aspect of the forecast will continue to be monitored. Stay tuned to the latest forecast updates as they become available.

Moisture is expected to linger into the start of the workweek, with PWAT values remaining near seasonal levels through Monday. This pattern will favor generally fair weather conditions during the morning hours, followed by the development of isolated to scattered afternoon showers, mainly across western Puerto Rico due to local and diurnal effects. Thereafter, moisture levels are expected to decrease below climatological normals around Tuesday. Across the U.S. Virgin Islands, mostly fair weather conditions are expected for much of the period. By Wednesday or Thursday, a patch of moisture embedded within the trade winds may bring a modest increase in shower activity across portions of the area.

In terms of temperatures, forecast 925-mb temperatures indicate a gradual trend toward more seasonal values from Sunday into the workweek, which should help moderate daytime temperatures somewhat compared to recent days. Even so, heat index values may continue to reach elevated levels across lower elevations and urban areas, particularly during periods of abundant sunshine.

AVIATION

(18Z TAFS) Issued at 301 PM AST Thu Jun 4 2026

Mainly VFR conditions throughout the period. ESE winds will continue up to around 15 kts with higher gusts. Area of cloudiness will continue over the eastern region while -SHRA/SHRA continues to move over the eastern and northern terminals, these can promote brief MVFR conditions particularly over JBQ through 04/22Z. Brief reductions in VIS due to HZ possible. ESE winds will decrease to around 10 kts after 04/23Z, increasing again after 05/13Z. Passing -SHRA will continue to reach windward sectors from time to time.

BEACH FORECAST

Issued at 301 PM AST Thu Jun 4 2026

Strong breezy will maintain a moderate rip current risk through at least the middle of next week for the beaches along the north, east and southeast of Puerto Rico, Vieques, Culebra and the Virgin Islands. The risk along western and southwestern Puerto Rico will be low. Life-threatening rip currents remain possible in the surf zone under a moderate risk.

FIRE WEATHER

Issued at 301 PM AST Thu Jun 4 2026

Clouds have increased in coverage this afternoon along eastern southern portions of Puerto Rico under a southeasterly flow. For most stations, relative humidities stayed in the 60-70%, with winds below 15 mph. The exception was Cabo Rojo RAWS, with values of 55% and winds of 15 mph for at least an hour. Taking these factors into consideration, the risk for fire spreading is low.

CLIMATE

Issued at 301 PM AST Thu Jun 4 2026

Rainfall deficits are building up in portions of Puerto Rico and the Virgin Islands. Some areas are experiencing rainfall deficits of 70 to 90%, especially along southwest and south-central Puerto Rico. In these areas, the demand of water for agricultural purposes has increased. These deficits, along with strong winds and summer heating led to the introduction of Moderate Drought (D1) conditions.

In the Virgin Islands, the month of May was also drier than normal. USGS monitored wells continue to experience water depletion. For this reason, D1 also developed in St. Croix, while St. Thomas and St. John currently experience Abnormally Dry conditions (D0).

SJU WATCHES/WARNINGS/ADVISORIES

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