textproduct: San Juan

KEY MESSAGES

Issued at 1252 PM AST Mon Oct 12 2026

- Expect, limited to elevated flooding threat through at least midweek due to increasing moisture and atmospheric instability as a mid-to-upper level low continues over and west of the islands.

- Limited heat risk for Puerto Rico and the US Virgin Islands through the workweek, please continue to monitor the forecast for any updates.

- Weaker winds on Tuesday will favor slower moving thunderstorms and higher localized rainfall totals across Puerto Rico and the US Virgin Islands.

- Moderate rip current risk will prevail along the northern and eastern beaches of Puerto Rico and Saint Croix from Tuesday onwards, elsewhere low rip current risk.

Short Term(This evening through Wednesday)

Issued at 1252 PM AST Mon Oct 12 2026

A relatively moist, unstable air mass will remain entrenched across the region for the next few days, while an upper-level low southwest of the region slowly moves north across Hispaniola through the short- term period. Recent soundings and satellite moisture tracking indicate total precipitable water values hovering between 1.90 and 2.10 inches, well above mid-October climatological normals. This abundant moisture, coupled with surface CAPE above 2000 J/kg and a light southeasterly low-level wind profile, will promote deep convective development this afternoon, mainly from north-central to western Puerto Rico. Weak steering winds will promote slow-moving showers and increase the threat of urban and small-stream flooding. The upper low will promote divergence aloft and colder-than-normal mid-level temperatures, which can produce strong thunderstorms that may produce small hail, gusty winds, and frequent cloud-to-ground lightning.

Through Tuesday, strong diurnal heating, sea breeze convergence, and terrain interaction will drive the weather along favorable upper- level dynamics. Afternoon showers and thunderstorms will concentrate primarily across the interior and western Puerto Rico, as well as downwind of the U.S. Virgin Islands. High-resolution model guidance indicates rainfall accumulations of 1.50 to 2.50 inches, with the highest totals over western PR. Given the soil moisture content across the western municipalities, urban and small-stream flooding alongside rapid river rises will remain the main hazards. Shower coverage is expected to trend downward by Wednesday as mid-level moisture slightly diminishes gradually. However, isolated heavy showers and thunderstorms are still expected over west-southwest PR as winds gradually shift more east to northeast from late Tuesday through Wednesday.

Across coastal and urban areas, light winds and high surface dewpoints will keep conditions humid. Daytime highs in the upper 80s to lower 90s will push heat indices above 100F daily, with localized areas in northern and western Puerto Rico briefly exceeding 105F. However, given the expected weather and ENE winds, heat advisory conditions are not expected across the islands.

Long Term(Thursday through next Sunday)

Issued at 1252 PM AST Mon Oct 12 2026

Stable conditions should prevail through the end of the workweek, then become wetter and unstable by early next week. A frontal boundary that induces a prefrontal trough north of the CWA should maintain an E-ENE wind flow on Thursday and Friday, briefly shifting to E-SE on Saturday as a surface high pressure exiting eastern CONUS builds over the Western Atlantic, then back to E-ENE by Sunday. In the mid to upper levels, a ridge north of the region should bring more stable conditions, with warmer-than-normal mid-level temperatures (up to -4 C), leading to subsidence across the area, unfavorable for deeper convection. However, the vicinity of a departing upper-level low, abundant moisture (PWATs around 1.75) in the low and mid levels combined with local effects could aid afternoon convection over western/southwestern Puerto Rico. Friday is forecast as the less active day of the period, as a drier slot in the mid levels (between 30 and 40 %), limiting shower activity. Afternoon convection can still be expected, though thunderstorms, if any, should remain isolated and short-lived. Although the dry mid- levels could persist on Saturday and guidance suggests low wind shear in the low to mid levels, E-SE winds should enhance daytime heating and the sea breeze convergence effect, along with the vicinity of an upper-level low, leading to isolated showers and thunderstorms over northwestern Puerto Rico. Conditions may gradually deteriorate by Sunday morning, as guidance suggests the approach of another retrogressive TUTT into the Caribbean, introducing instability. The latest model solutions suggest slightly colder than normal mid-level temperatures (below -7 C), with an increase in moisture content in the mid levels and steeper lapse rates. Under this scenario, an advective pattern is likely on Sunday morning across windward sections of the islands, followed by deep convection across interior and western Puerto Rico and local island streamers.

Overall, showers and thunderstorms can be expected each day, with less chance of flooding on Friday. On Thursday and Saturday, mainly ponding of water over roadways and poorly drained areas is expected, with minor flooding. With the approach of the retrogressive TUTT, Sunday is likely to be the wettest day of the period, increasing the chance of urban and small stream flooding across western Puerto Rico.

AVIATION

(18Z TAFS) Issued at 1252 PM AST Mon Oct 12 2026

Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. However, +SHRA/TSRA over western PR may cause tempo MVFR to brief IFR conds at TJBQ thru 12/22z. Elsewhere, mostly VCSH expected. The 12/12z TJSJ sounding indicated ESE winds up to 20 kt blo FL030. Light and variable winds expected overnight, bcmg E-ENE at 10-15 kt aft 13/13z.

MARINE

Issued at 1252 PM AST Mon Oct 12 2026

Lingering upper-level low will continue to promote showers and isolated thunderstorms across the regional waters through midweek. High pressure over the central Atlantic will maintain moderate east- southeast winds, though winds will gradually diminish through Tuesday. Choppy seas will persist across portions of the offshore Caribbean and Atlantic waters before gradually improving. Lighter east to east-southeast winds and generally lower seas are expected from Tuesday into midweek. Mariners should remain alert, as thunderstorms may locally produce gusty winds, higher seas, frequent lightning, and reduced visibility.

BEACH FORECAST

Issued at 1252 PM AST Mon Oct 12 2026

Low rip current risk through tonight across the beaches of Puerto Rico and the U.S. Virgin Islands. Although the overall risk is low, localized rip currents can still occur, particularly near jetties, piers, and other structures. Beachgoers should continue to exercise caution in the surf zone. From late Tuesday onwards, moderate rip current risk will prevail mainly over the northern and east facing beaches of Puerto Rico, Culebra, potentially Saint Croix.

SJU WATCHES/WARNINGS/ADVISORIES

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