textproduct: San Juan

KEY MESSAGES

Issued at 345 AM AST Thu Oct 8 2026

- Lingering moisture from the departing tropical wave, combined with a southeasterly flow, will promote afternoon showers and thunderstorms across interior and western Puerto Rico, as well as the eastern and metropolitan areas.

- As a result, the flood risk will remain limited to elevated in those areas, particularly with the stronger rain activity during the afternoon hours.

- Isolated lowlands, urban and coastal areas, as well as locations that do not receive rainfall, may experience briefly elevated heat indices before afternoon showers and thunderstorms develop.

- Drier conditions are expected by Friday, with a return to a more seasonal weather pattern by Saturday. However, models suggest that atmospheric instability may increase again from Sunday into early next week. Stay tuned to the latest forecast.

- A moderate risk of rip currents is expected through today along portions of the north and east-facing beaches of the islands. A lower risk is forecast to return Friday and continue through the weekend.

Short Term(Today through Saturday)

Issued at 345 AM AST Thu Oct 8 2026

Predominantly fair conditions prevailed during the overnight hours. Advective showers remained mainly over the offshore waters with some affecting portions of the US Virgin Islands and eastern Puerto Rico. Accumulations estimated by the radar remained below 4 deciles of an inch over land. Minimum temperatures ranged in the mid 70s to low 80s across coastal and lower elevation regions of the US Virgin Islands and Puerto Rico, while they ranged in the mid 60s to low 70s along the mountainous interior of Puerto Rico.

Today the lingering moisture from the departing tropical wave should provide the necessary instability for another active weather day. Precipitable water (PWAT) values will remain above seasonal levels favoring the development of showers across the region. Model guidance also indicates that the atmospheric column will be moist favoring the development of deep convection. While a couple of mid- level high pressure systems are still acting to warm and lower lapse rates at these levels, the available moisture coupled with local effects and a breezy ESE steering flow set by a surface-level high pressure should still lead to the development of convective activity. In contrast to the pattern observed yesterday, the activity today should be more seasonal with the US Virgin Islands and eastern Puerto Rico receiving rainfall associated to streamers from el Yunque and the smaller islands during the afternoon and from advective showers during the night and morning hours. Whereas, showers and thunderstorms will develop along the western interior and northwestern Puerto Rico during the afternoon. The soil may be saturated over some regions that have received heavy rainfall over the past 24 hours. Thus, there is an elevated flooding risk for areas where frequent downpours occur. This means that flooding in urban areas, roads, small streams and washes as well as a low chance for flash floods is possible. With increased cloud cover, lower minimum temperatures, and a breezy windflow, the heat risk for today is limited. Some urban and exposed regions that do not receive rain may experience brief periods of elevated heat indices. Individuals are invited to remain updated in case there are changes to the forecast during the day.

Friday is forecasted to be the least active day of the short term period. Dry air will gradually filter into the region bringing PWAT values to below seasonal levels as well as dry mid-to-upper levels. The low-level high pressure will move away from the region, thus the steering flow will shift to be from the E during the morning and from the ENE during the afternoon. This shift in wind flow should also aid in bringing cooler and drier air to the region. With a breezy steering flow and local effects, showers and thunderstorms may still develop. However these will have a seasonal pattern with the focus of the rain being over the southwest portion of Puerto Rico during the afternoon. The flooding risk for the day is thus limited. This means that ponding of water in roads and poorly drained areas is possible. Given these conditions, the heat risk for the day remains limited.

Saturday will be denoted by a transitioning period to a more active weather pattern. This will be caused by a surface-induced trough that will gradually approach the region and remain to the NE of the islands. This will cause the mid-level temperatures to quickly cool from the morning into the afternoon, setting a more favorable environment for the development of deep convective cells. The surface-induced disturbance will also help set the steering flow to be from the ENE. While some areas may experience locally breezy conditions, the windflow will slightly slow down increasing the potential for showers to linger over the regions they occur. PWAT and column relative humidity values should also increase from the morning into the afternoon further promoting the development of showers and thunderstorms. Thus, the flooding risk for the day is elevated. These conditions will lead to a limited heat risk on Saturday. Consequently, Saturday should set the scene for a more active long-term period.

Long Term(Sunday through Thursday)

Issued at 345 AM AST Thu Oct 8 2026

An upper-level low is forecast to meander over the region through the long term forecast. This will cause unstable conditions aloft as 500 mb temperatures drop to -7/8 degrees Celsius through most of the period. This cooling aloft will produce steep mid-level lapse rates and in addition, a 250 mb jet will provide strong upper-level divergence and ventilation that can support deep, organized convection each day. At the surface, moderate to locally fresh trades are expected through Monday as a surface high pressure moves over the western Atlantic and an induced low-level trough moves from east to west across the islands. Lighter ESE winds are expected thereafter through midweek.

A gradual pooling of moisture is expected across the eastern Caribbean as the low moves south of the islands and winds veer from southeast. Precipitable water content is expected to range between 1.75-2.10 inches through the forecast period. A saturated atmospheric column with deep instability and strong upper-level lift can produce multiple rounds of heavy showers and intense thunderstorms. Consequently, there will be an elevated threat of urban and small-stream flooding, localized flash flooding, strong gusty winds, and frequent lightning. While daytime heating and local effects will still focus the most intense, slow-moving convection over the interior and western portions of Puerto Rico, the broad synoptic forcing will also bring periods of locally heavy rainfall and strong thunderstorms to the USVI and eastern PR.

AVIATION

(06Z TAFS) Issued at 345 AM AST Thu Oct 8 2026

VFR conds expected through most of the forecast period. Passing VCSH across TJSJ and the USVI sites early today. Aft 08/17Z, SHRA/+TSRA are expected to develop across the interior into W PR, producing effects at TJBQ/TJPS, and streamers may also briefly affect TJSJ. As a result, intermittent/brief MVFR/IFR conds due to VIS reductions, lower CIGS, and mountain obsc. ESE winds will increase to 10-15 kt, with typical sea breeze variations, then becoming light/VRB aft 08/23Z.

MARINE

Issued at 345 AM AST Thu Oct 8 2026

Weak surface high pressure over the central Atlantic continues to drift eastward, displaced by a frontal boundary moving east across the western Atlantic. This is resulting in weak pressure gradient, maintaining mainly gentle to moderate easterly trade winds. Another surface high- pressure system will build across the western Atlantic over the weekend, sustaining the easterly trade winds. Meanwhile, residual moisture from a departing tropical wave will fuel additional rounds of showers and thunderstorms today, with the potential for locally strong gusty winds, higher seas, and waterspouts.

BEACH FORECAST

Issued at 345 AM AST Thu Oct 8 2026

Moderate risk of rip currents today along the north- and east-facing beaches of Puerto Rico, as well as Culebra, and the U.S. Virgin Islands. Low risk returns Friday onwards for all local beaches.

Shower and thunderstorm activity associated to the departing tropical wave will maintain the lightning risk across the area today. Locally gusty winds are also possible near thunderstorms.

SJU WATCHES/WARNINGS/ADVISORIES

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