textproduct: San Juan

KEY MESSAGES

Issued at 256 PM AST Wed Jun 10 2026

* A wetter and more unstable weather pattern is expected tomorrow as a tropical wave interacts with an approaching upper-level trough, increasing the coverage of showers and thunderstorms across the region and posing the greatest risk of flooding on Thursday.

* Hot heat indices will continue through much of the week. Heat indices may exceed 100F, especially across urban, coastal, and lower-elevation areas of Puerto Rico and the U.S. Virgin Islands. Heat Advisories may be needed at times.

* Another air mass with Saharan dust will persist through the forecast period, producing somewhat hazy skies and reduced air quality, especially trailing the wave late on Thursday night or early Friday morning into early Saturday.

* The potential for life-threatening rip currents will turn moderate from Thursday onward, first across St Croix, then spreading to the rest of the east and north-facing beaches in the USVI and PR.

Short Term(This evening through Friday)

Issued at 256 PM AST Wed Jun 10 2026

Another quiet day under warm, hot conditions, with heat indices between 100 and 102, and isolated higher values in many coastal and urban locations in PR and the USVI. The Doppler radar observed little or no rain this morning. Air temperatures ranged from the upper 80s to the low 90s along PR and the USVI's coastal areas, to the low 80s in mountain areas. Winds were mainly from the east at 10 to 15 mph, with higher gusts and sea-breeze variations.

Heat indices remain dangerous for vulnerable communities this afternoon, especially along the north and west coast of PR and the U.S. Virgin Islands. The proximity of a polar trough, combined with excessive heating, variations in sea breezes, and local factors, will lead to showers and possibly isolated thunderstorms, especially in the interior or western regions of Puerto Rico. Thus, we have a limited flooding risk for these locations. The rest of the islands will experience little or no rain.

Thursday seems the better day for widespread rain, as a polar trough amplifying near the northeast Caribbean will enhance instability and the potential for thunderstorms. Although the potential for warm and hot temperatures will persist on Thursday, there is a greater chance of urban and small-stream flooding, along with isolated flash flooding, as the tropical wave interacts with the polar trough lingering aloft. Some limiting factors associated with the weather pattern include potential cloud cover from the mid- to upper-level trough, which could inhibit afternoon convection and decrease the heating we experience. Therefore, we encourage our residents and visitors to monitor weather conditions, as we will update them as conditions require.

The intrusion of dry air, later around Thursday night into early Friday morning, trailing the tropical wave, will increase Suspended Saharan Dust Particles across the islands, potentially leading to another episode of hazy skies. However, typical trade wind showers will remain possible, followed by afternoon convection.

LONG TERM

Issued at 132 AM AST Wed Jun 10 2026

In general, drier air with embedded patches of moisture will filter into the region steered by up to breezy E to ESE flow (backing to become more easterly late in the period). This will steer showers over windward sectors and, with diurnal heating and local effects, help develop shallow afternoon convection over western/northwestern Puerto Rico. Additionally, lines of showers can also develop downwind of the local islands and El Yunque. Ponding of water over roadways and poorly drained areas continues to be possible. Discrepancies continue between the GFS and ECMWF model guidance to start the workweek, with the GFS suggesting an upper-level trough lingering near the region and above normal PWAT values and the ECMWF suggesting more mid-level ridging and generally drier air. The GFS seems to lean more towards a ridging pattern than yesterday; a more seasonal pattern was added to start the next week. 925 mb temperatures are forecast to continue at or above normal, prompting a limited to possible elevated heat risk each late morning to late afternoon. Heat indices can reach and exceed 100 degrees Fahrenheit at urban and lower elevations areas of the islands. Saharan Dust will continue to filter over the local islands during the long term period. Current model guidance also suggests higher concentrations approaching the islands after the long term period.

AVIATION

(18Z TAFS) Issued at 256 PM AST Wed Jun 10 2026

VFR conditions will prevail tonight. SHRA/-SHRA will develop along the Cordillera Central between 19-23z, which could impact the vicinity of JBQ. Winds will continue from the E-ESE at 10 to 15 knots with sea breeze variations through 10/23z. After that, we expect calm to light and VRB winds with land breeze variations. A tropical wave will increase the chance of TSRA/SHRA near terminals, beginning near IST/ISX/JSJ around 10/10-15z, spreading to PR terminals from 10/12z onward.

MARINE

Issued at 256 PM AST Wed Jun 10 2026

Mariners can expect moderate easterly winds, resulting in moderate chop across the surrounding waters tonight into tomorrow. An induced surface trough near the region interacting with a weak tropical wave will provide a better chance for thunderstorm formation across the PR and the USVI regional waters around Thursday. The Azores high will build across the central Atlantic, promoting the return of the east-southeast winds late in the workweek into the weekend.

BEACH FORECAST

Issued at 256 PM AST Wed Jun 10 2026

The rip current risk is low for the rest of tonight and tomorrow for PR and the northern USVI. However, life-threatening rip currents may still occur, especially near groins, jetties, reefs, and piers. Meanwhile, St Croix will have a moderate chance of rip currents tomorrow, spreading to the rest of the USVI and PR by Thursday.

Thunderstorms will be possible across the northwest quadrant of PR this afternoon, with the potential for thunderstorms increasing around Thursday across most beaches in PR and the USVI.

FIRE WEATHER

Issued at 256 PM AST Wed Jun 10 2026

Expect a LOW fire weather risk across the southern sections of the islands, as brief conditions will be present.

SJU WATCHES/WARNINGS/ADVISORIES

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