textproduct: San Juan

KEY MESSAGES

Issued at 123 PM AST Thu Oct 1 2026

* A disturbance will aid in the formation of showers and t-storms this afternoon, mainly over interior to western Puerto Rico, while streamers, and showers and t-storms from the Caribbean Waters, move over the southern and eastern regions.

* Lingering moisture and more favorable conditions will result in stronger t-storms Friday and Saturday. This will sustain a flooding risk, especially over interior to western Puerto Rico where an elevated flooding risk will persist each afternoon.

* Heat risks will also persist through the rest of the week, possibly becoming elevated tomorrow, Friday, particularly across coastal urban areas of northern and western Puerto Rico and areas of the U.S. Virgin Islands.

* A moderate risk of rip currents will continue along northern, and eastern beaches of Puerto Rico, as well as across portions of the U.S. Virgin Islands.

Short Term(This evening through Saturday)

Issued at 123 PM AST Thu Oct 1 2026

A surface-induced disturbance filtered into the US Virgin Islands and Puerto Rico overnight bringing from average-to-above average precipitable water values to the region. The bulk of this moisture remains situated to the southeast of the islands and will continue to move across the region during the day. The associated moisture combined with breezy conditions has already lead to the development of advective showers, affecting portions of the US Virgin Islands, windward waters and eastern Puerto Rico. Radar estimates indicate that municipalities like Yabucoa, Maunabo, Patillas, Naguabo, Fajardo and Humacao have already received 0.5-1 inches of rain as convection continues to progress over the region. Lingering moisture from the disturbance will persist over the CWA until Saturday promoting the development of passing showers and localized thunderstorms. A couple of high and low pressure systems located over the west and central Atlantic Ocean are setting the steering flow to be from the ESE until the end of the short term period. This is expected to promote breezy-to-locally windy conditions until Saturday which will serve as a drivers for advective showers during the mornings and streamers from el Yunque and the smaller islands during the afternoons.

Model guidance suggests that today will be characterized by a moister vertical profile during the afternoon. Additionally, while the day began with warmer than average mid-tropospheric temperatures, these will begin to decrease into the afternoon leading to a steepening of the 700-500 mb lapse rates. While an upper-level low pressure system continues to promote upper-level convergence near the islands, the aforementioned features combined with the enhanced moisture from the disturbance and breezy wind conditions will lead to streamers affecting the US Virgin Islands and eastern Puerto Rico this afternoon with showers and thunderstorms and showers over the Caribbean waters also affecting the southeast and south portions of Puerto Rico. In addition, coupled with local effects, the enhanced moisture availability will also lead to the development of convection across the interior, western interior, and western Puerto Rico during the afternoon. While the showers might move at a moderate pace, they might be recurrent over some regions. Thus, there is an elevated flooding risk wherever frequent downpours do occur. This means that flooding in urban areas, roads, small streams, and washes along with a low chance for isolated flash floods is possible.

With cooling aloft, steepening of the mid-tropospheric lapse rates, lingering moisture from the surface-induced disturbance and the departure of the upper-level low pressure system, Friday promises to be the most active day of the short term period. A similar pattern will persist with advective showers during the morning and streamers from El Yunque and the smaller islands affecting the US Virgin Islands and eastern Puerto Rico during the afternoons. Whereas, rainfall is expected to affect the western and northwestern region of Puerto Rico during the afternoon. The flooding risk remains elevated with a focus on the norwestern portion of Puerto Rico.

For Saturday, there is some disagreement in the models, with some suggesting a moister vertical column and others suggesting drier mid- levels. Nonetheless, lingering moisture, breezy ESE conditions, cooling aloft, steepening of the mid-tropospheric lapse rates, and local effects will favor the development of convection. By Saturday, the focus of the rainfall will be on the western interior and western Puerto Rico during the afternoon. Model guidance suggest that winds will back late afternoon into the evening. Please continue to monitor the forecast, an earlier change in the steering flow can affect the location of convection.

With and increase in precipitable water and low-level temperature values above normal values for the season the heat risk is expected to be limited for today and Saturday, with an elevated risk expected by Friday. These levels of heat may affect individuals sensitive to heat, without effective cooling and adequate hydration. Citizens and visitors are invited to remain alert of the changing weather conditions.

Long Term(Sunday through Thursday)

Issued at 353 AM AST Thu Oct 1 2026

A variable and seasonal pattern will persist for the first part of the long term. On Sunday, broad surface high pressure will remain in place across the central Atlantic through Sunday into Monday, while its combines with an induce disturbance over the central Atlantic, maintaining an easterly wind flow within the 03 km layer across Puerto Rico and the U.S. Virgin Islands. Aloft, a cut-off low anchored over the western Atlantic and Caribbean, just north of eastern Cuba, will enhance southerly winds at 250 mb, favoring the development of an extensive upper-level cloud deck over the islands. The influence of this upper-level low will also be evident at 500 mb, where southerly flow and slightly colder temperatures, near -7C to -8C, are expected. Despite the colder temperatures aloft, available moisture will remain limited, with PWAT values generally near climatological normals and most of the moisture confined to the lower levels. Therefore, although periods of upper-level cloudiness will persist, especially into Monday, the overall weather pattern should remain relatively stable with limited deep moisture available for significant convective development. On Monday, similar weather conditions will persist with possibly less upper cloudiness as the advecting upper-level moisture pattern with the high clouds moves out of the region. As a result, warmer temperatures and heat indices are possible, with a limited heat threat along the islands, with some isolated areas that have an elevated heat threat, especially in the coastal areas and urbanized areas.

On Tuesday, the mid-level ridge will still be present, marginally limiting deep convection. However, lapse rates returning to seasonal values signal a better chance of typical afternoon showers and thunderstorms driven by an easterly flow. This pattern should allow afternoon convection to move over the interior and then over western portions of Puerto Rico. A tropical wave will reach the islands by Tuesday evening, increasing the PWAT values to above-seasonal levels through Wednesday. Therefore, Wednesday is forecast to be the more active day in terms of shower and thunderstorm activity, supported by mid-level lapse rates at above-seasonal levels (exceeding 6.0 C/km). Additionally, a more east-southeasterly flow could drive further activity over northwestern PR. As a result, for Tuesday into Thursday there is a high chance of observer a limited to elevated flooding threat especially over western sections of Puerto Rico.

Overall, the primary hazards for the long-term period will remain a limited-to-elevated heat risk and a limited risk of excessive rainfall from Sunday through Tuesday. As a result, urban and small- stream flooding is possible over roadways and poorly drained areas, and flash flooding cannot be ruled out. For those sensitive to the heat, staying hydrated and avoiding outdoor activities during peak heating hours is highly recommended.

AVIATION

(18Z TAFS) Issued at 123 PM AST Thu Oct 1 2026

Mainly VFR conditions to prevail during the period. Developing VCTS over the region will affect mainly TJBQ/TJSJ/TJPS/TJBQ. Tempo MVFR conditions due to -TSRA are more likely at TJBQ btw 01/18-22Z. VCSH/-SHRA also affecting terminals during the afternoon, affecting more the eastern region overnight. ESE winds up to 15 to 20 kts, with higher gusts and sea breeze variations thru 01/21Z. Decreasing after 01/23Z, to up to around 10 kts with land breezes, before increasing again after 02/13Z.

MARINE

Issued at 123 PM AST Thu Oct 1 2026

A surface high pressure north of the region will maintain moderate to locally fresh easterly trade winds through at least Friday, producing choppy conditions across the Atlantic and Caribbean waters as well as local passages. Winds will shift to mainly moderate over the weekend and into early next week, keeping seas moderately choppy. Meanwhile, a passing disturbance today will increase showers and thunderstorms across the waters, creating locally hazardous conditions for small craft, including gusty winds, higher seas, lightning, and reduced visibility, with lingering moisture maintaining unsettled weather into the early weekend.

BEACH FORECAST

Issued at 123 PM AST Thu Oct 1 2026

A moderate risk of rip currents will persist across most exposed north- and east-facing beaches of Puerto Rico and the U.S. Virgin Islands through at least Sunday, before diminishing to low across all beaches Monday into Tuesday. Beachgoers should remain cautious, as dangerous rip currents can still occur near piers, jetties, groins, and rocky areas, always swim near a lifeguard and follow beach patrol guidance and posted warning flags. Additionally, afternoon thunderstorms may develop, particularly along western and northwestern Puerto Rico; if you hear thunder, immediately leave the water and seek shelter inside a substantial building or enclosed vehicle.

SJU WATCHES/WARNINGS/ADVISORIES

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