textproduct: San Juan

KEY MESSAGES

Issued at 335 AM AST Mon Oct 5 2026

- Hot and humid conditions are expected today before afternoon convection develops. A Heat Advisory is in effect from 10 AM to 3 PM AST across Puerto Rico and the U.S. Virgin Islands.

- Afternoon showers and thunderstorms will develop today, mainly across interior and western Puerto Rico, with a limited to elevated flood risk. Coverage will increase Tuesday. Passing showers will also affect eastern Puerto Rico and the U.S. Virgin Islands overnight/mornings.

- An approaching tropical wave will bring a wetter and more active weather pattern from Wednesday into Thursday. This could increase the risk of locally heavy rainfall, flooding, and stronger thunderstorms.

- A low risk of rip currents is expected today, with a moderate risk returning Tuesday through Thursday along portions of the north and east-facing beaches of the islands.

Short Term(Today through Wednesday)

Issued at 335 AM AST Mon Oct 5 2026

Passing advective showers have developed overnight along the windward waters, US Virgin Islands and eastern Puerto Rico leaving accumulations of around 0.8 inches (e.g., offshore waters, Ceiba, Fajardo, and Luquillo). Overnight minimum temperatures have been ranging between from mid 70s to low 80s along coastal areas while in the upper 60s to low 70s across the interior and higher elevation terrain. The windflow has been light and from the ESE. Satellite imagery shows mostly cleared to partly cloudy skies in some areas.

The short term will be characterized by a variable weather pattern. By today as the uper-level low pressure system currently south of La Hispanola moves further away from the region and a mid-level ridge settles north of the islands, there will be warming around 500 mb, which will consequently cause a decrease in the lapse rates at these levels. This synoptic feature will act to inhibit the development of deep convective cells. The mid-levels will also be dominated by drier air further inhibiting the development of convection. Lower than average to average precipitable water (PWAT) values will also be present over the region. Thus, while weather is still expected to develop during the day, it will be driven by local effects and the weak ESE wind flow. Rainfall from advective showers during the night and morning and streamers from el Yunque and the smaller islands during the afternoon is expected to impact the US Virgin Islands and northeastern Puerto Rico. Whereas, passing showers and localized thunderstorms are expected to affect portions of the western interior and northwestern Puerto Rico during the afternoon. Given the slow winds, wherever showers linger and/or produce frequent downpours an elevated flooding risk is possible. This means that flooding in urban areas, roads, small streams and washes, along with a risk for isolated flash floods is possible.

A similar weather pattern is expected by Tuesday, with conditions predominantly driven by local effects. A distinct feature for the day will reside in a more humid vertical profile and above average PWAT values. This will result in passing showers and localized thunderstorms particularly over the western interior and the northwestern portions of Puerto Rico during the afternoon. Nonetheless, passing advective showers and streamers may also affect the US Virgin Islands and eastern Puerto Rico. An elevated flooding risk is also expected where frequent downpours occur.

By Wednesday morning into the afternoon, conditions will become more variable across the CWA as a tropical wave will pass over the islands bringing above average PWAT values to the region. This will lead to a moister vertical column and consequently, to a more active day in terms of shower and thunderstorm activity. Rainfall is expected to be more widespread and affect portions of the US Virgin Islands and eastern Puerto Rico during the morning and interior and western Puerto Rico during the afternoon. The slower winds will also increase the flooding potential as the showers that develop may linger increasing the chance of higher rainfall accumulation. The flooding risk will be higher over areas that may be saturated from rain received over Monday and Tuesday. Citizens and visitors are invited to keep monitoring weather conditions as they evolve and forecast updates become available.

With lower than average winds, seasonal PWAT values, 925 mb temperatures two standard deviations above average, and lower cloud coverage during the morning and early afternoon, the heat risk for today and Tuesday are elevated. With the passage of the tropical wave and increased cloud coverage the heat risk for Wednesday is expected to become limited. These levels of heat may affect individuals sensitive to heat, without effective cooling and adequate hydration.

Long Term(Thursday through Sunday)

Issued at 335 AM AST Mon Oct 5 2026

Moisture associated with a departing tropical wave will linger across the local region on Thursday. Combined with modest mid- level enhancement, another active afternoon is forecast on Thursday, with scattered to numerous showers and isolated thunderstorms across the interior, western, and northwestern sections of Puerto Rico. Steering flow will remain predominantly southeasterly before turning easterly. An elevated flood threat will persist across interior and western Puerto Rico, while a limited flood threat continues for eastern Puerto Rico and the U.S. Virgin Islands as frequent passing showers will continue to affect those areas Thursday into Thursday night. Some of the activity may be accompanied by gusty winds.

A transition to drier and more stable conditions is forecast on Friday as mid-level ridge builds just north of the region. This will support mid-level warming, decreased lapse rates, and drier air aloft, making Friday the most stable day of the long-term period. The 500 mb temperatures are forecast to be around -4 degrees Celsius, which is near two standard deviations above normal for this time. Nevertheless, diurnal convection driven by daytime heating and local effects will still support afternoon showers across interior to western Puerto Rico. On Saturday, stable conditions aloft will generally persist, though a slight increase in moisture will bring typical seasonal passing showers over windward areas during the overnight and morning hours, followed by afternoon convection across interior to western portions of Puerto Rico.

By Sunday, the mid-level ridge retreats as a mid- to upper-level trough approaches the region from the east. The resulting cooling in the mid-troposphere and increasing atmospheric instability will support more active afternoon convection across the islands. Rain streamers remain possible downwind from El Yunque, Vieques, Culebra, and the U.S. Virgin Islands throughout the period. Additionally, an elevated heat threat will persist each day, and heat advisories could be issued. Continue to monitor for any updates on the forecast.

AVIATION

(06Z TAFS) Issued at 335 AM AST Mon Oct 5 2026

Mainly VFR conds are expected across all terminals through the forecast period. Passing -SHRA/VCSH across TJSJ and the USVI terminals during the morning hrs. Aft 05/17Z, SHRA/TSRA are expected to develop across the interior into W/NW PR, producing VCTS at TJBQ/TJPS, and streamers may also affect TJSJ. Intermittent/brief MVFR conds due to vis reductions, lower cigs, and mountain obsc. ESE winds will increase aft 13Z to 10-12 kt, with typical sea breeze variations. Light and variable winds return overnight.

MARINE

Issued at 335 AM AST Mon Oct 5 2026

The surface high over the western Atlantic continues to move east, as a low (frontal boundary) makes its way into the western Atlantic, easing the pressure gradient and resulting in light to moderate east to east-southeast winds. Winds will increase somewhat Tuesday into Wednesday as another surface high builds over the western Atlantic. Seas will range from 3 to 4 feet, occasionally higher. A tropical wave crossing late Wednesday into Thursday will increase shower and thunderstorm activity.

BEACH FORECAST

Issued at 335 AM AST Mon Oct 5 2026

Low rip current risk through Monday night and gradually becoming moderate particularly along the north and east-facing beaches of Puerto Rico, Vieques, Culebra and the US Virgin Islands from Tuesday onwards. However, life-threatening rip currents can still occur near groins, jetties, reefs, and piers. The low risk is expected to return Friday into the weekend. Keep in mind that the daily afternoon lightning risk will also affect local beaches, primarily across northern and western Puerto Rico.

SJU WATCHES/WARNINGS/ADVISORIES

PR...Heat Advisory from 10 AM this morning to 3 PM AST this afternoon for PRZ001>013.

VI...Heat Advisory from 10 AM this morning to 3 PM AST this afternoon for VIZ001-002.

AM...None.