textproduct: San Juan

KEY MESSAGES

Issued at 335 AM AST Sun Oct 11 2026

- An unsettled pattern will support daily showers and thunderstorms through the first part of the week, with a more seasonal pattern expected the second part of the week.

- A limited to elevated flood risk will persist through Thursday. Heavy rainfall may cause urban and small stream flooding, with localized flash flooding possible.

- Weaker winds Tuesday and Wednesday may favor slow-moving thunderstorms and higher localized rainfall totals, especially along the Cordillera Central and across interior to northwestern Puerto Rico.

- Stronger thunderstorms may produce frequent lightning and strong wind gusts, creating hazardous conditions on land, along beaches, and across the local waters.

- A moderate rip current risk may persist today across exposed northern and eastern beaches. The risk is expected to decrease Monday but could increase again by midweek. Seek shelter immediately if thunder is heard.

Short Term(Today through Tuesday)

Issued at 335 AM AST Sun Oct 11 2026

Subsidence associated with a retrograding mid- to upper-level low suppressed shower activity across the islands through midnight. However, showers and thunderstorms remained mainly over the local waters, and some moved across the USVI and eastern PR. Temperatures ranged from the lower to upper 70s across most coastal locations and from the lower to mid 60s in portions of the mountains. Winds were generally calm or light and variable, with localized land- breeze fluctuations.

A mid- to upper-level trough, combined with sufficient tropical moisture, will keep conditions unsettled through at least Tuesday. Forecast 500-mb temperatures near 8C Sunday into Monday, below the climatological 25th percentile, will favor enhanced instability. Lapse rates will vary by layer and time, with the 850700-mb layer becoming progressively steeper into Tuesday. These conditions will support showers and thunderstorms, particularly in the afternoon and evening, with additional activity possible overnight into early Monday morning. Stronger thunderstorms may produce frequent lightning, gusty winds, and locally heavy rainfall.

Through Monday, model guidance indicates generally near-normal low- level wind speeds, with 925-mb winds around 16-20 mph (14-17 kt) before weakening late Monday. The expected east-southeast flow will favor showers and isolated thunderstorms across eastern Puerto Rico, Vieques, Culebra, and the U.S. Virgin Islands overnight and into the morning. Although faster-moving convection could limit rainfall duration at individual locations, repeated rounds of heavy rainfall may still produce ponding and localized urban and small-stream flooding. Afternoon and evening convection will favor interior and northwestern Puerto Rico, where isolated flash flooding cannot be ruled out. Flood risk remains limited to elevated.

On Tuesday, despite gradual warming at 500 mb, steep 850-700 mb lapse rates, increasing 700-500 mb relative humidity, and weaker low- level winds will maintain conditions favorable for convection. Daytime heating, sea-breeze convergence, and orographic lifting will favor initial development along the Cordillera Central, with subsequent development influenced by local circulations and outflow boundaries. If weak steering flow supports slow-moving or repeatedly developing thunderstorms, localized rainfall accumulations and flooding potential could increase, including the possibility of isolated flash flooding.

Long Term(Wednesday through Sunday)

Issued at 335 AM AST Sun Oct 11 2026

The retrograding mid-to-upper-level low will dominate the area through Thursday before exiting by the end of the long-term period, promoting more seasonal conditions. Latest guidance still suggests 500 mb temperatures will drop below -7 degrees Celsius on Wednesday and Thursday, causing steep mid-level lapse rates. Associated with this synoptic feature, an induced inverted surface trough will continue to favor low-level convergence and seasonal to above-normal PWAT values around 1.85 to 2.25 inches. Combined with daytime heating and local effects, this could support deep, organized convection through Thursday. By Friday and Saturday, a more seasonal pattern is expected as the mid-to-upper-level low exits the area; hence, less moisture is anticipated, particularly in the mid-levels. However, local effects and lingering low-level moisture could still promote shower and thunderstorm activity.

On Wednesday, light to gentle east-southeasterly winds will favor slow-moving showers and thunderstorms, primarily over the interior to northwestern sections of Puerto Rico. By Thursday, model guidance still suggests a frontal boundary exiting the eastern CONUS and inducing a pre-frontal trough north of the CWA. This will shift winds to an ENE flow on Thursday, focusing convection over the interior and southwestern Puerto Rico. By the end of the period, winds are expected to shift gradually to an east to east- southeasterly flow, driving activity mainly toward interior and western Puerto Rico on Friday, and northwestern sections from Saturday onwards. Regardless, passing showers and thunderstorms cannot be ruled out across eastern Puerto Rico and the USVI each day.

These conditions will maintain a limited to elevated risk of flooding through Thursday, with urban and small stream flooding and flash flooding possible, particularly on Wednesday, when lighter winds will favor slow-moving showers with higher rainfall accumulations. In addition, localized strong wind gusts and frequent lightning are expected with the strongest thunderstorms.

AVIATION

(06Z TAFS) Issued at 335 AM AST Sun Oct 11 2026

Mainly VFR conds should prevails across all TAF sites, though prds of -TSRA/+TSRA associated with a trough apch the CWA may reduce CIGs/VIS and bring tempo MVFR/IFR conds across eastern TAF sites btwn 11/06-11/12z. Afterward, VCTS can be expcd across most terminals, with PROB30s over JPS due to aftn cnvtn that may reduce CIGs/VIS. Winds should pick up btwn 10 - 15 kt and gusts up to 22 - 25 kt aft 11/12z. LLWS cannot be ruled out during the fcst prd.

MARINE

Issued at 335 AM AST Sun Oct 11 2026

A mid- to upper-level trough and its associated surface trough will promote showers and isolated thunderstorms across the regional waters through early this week. High pressure over the central Atlantic will maintain moderate to locally fresh east-southeast winds through Monday, producing moderately choppy to choppy seas. As high pressure shifts farther east, the pressure gradient will relax, allowing winds to diminish to light to gentle breezes Tuesday and Wednesday. High pressure building across the western Atlantic behind a cold front will favor east-to-east-northeast flow later in the week. Thunderstorms may produce locally higher winds and seas, lightning, and reduced visibility.

BEACH FORECAST

Issued at 335 AM AST Sun Oct 11 2026

Some changes were introduced to the beach forecast, as a moderate risk of rip currents may persist today. Although the latest nearshore buoys continue to report seas between 2 and 3 feet, winds should remain between 10 - 15 kt, gusts up to 20 - 25 kt. Therefore, this moderate risk is expected across northern and eastern exposed beaches of the islands. Beachgoers must exercise caution, as life- threatening rip currents remain possible along the surf zone. The risk should lower by Monday, though it may upgrade by mid week. As mentioned in the previous discussion, beachgoers should remain weather alert as showers and thunderstorms are expected each day, most active early this week across the islands. Thunderstorms approaching coastal areas may bring periods of heavy rainfall, gusty winds, and lightning. Beachgoers must seek for shelter whenever they hear thunder.

SJU WATCHES/WARNINGS/ADVISORIES

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