textproduct: San Juan

KEY MESSAGES

* An elevated risk of flooding will continue to prevail today across much of Puerto Rico as a trade wind perturbation moves across the forecast area.

* For the U.S. Virgin Islands, although passing showers and thunderstorms may lead to ponding of water on roads today, the main hazard is the heat risk with heat indices exceeding 100 degrees F.

* Across Puerto Rico and the U.S. Virgin Islands, the heat indices may briefly meet or exceed 108F today; nevertheless, under easterly winds and cloudiness associated with the passing perturbation, most of the time must remain below the Heat Advisory Criteria.

LONG TERM...Wednesday through Sunday

A weakening in the mid-level ridge pattern is expected early in the cycle as trofiness develops northeast of the local islands. However, by the end of the cycle, the mid-level ridging will return. At lower levels, a surface high pressure will prevail across the tropical Atlantic, promoting east- southeast winds. Based on the latest grand ensemble, precipitable water is expected to remain above 2.0 inches from Wednesday through Friday, with a sharp decrease anticipated over the upcoming weekend as the developing mid-level ridge erodes the available moisture. The highest values of precipitable water early in the forecast cycle coincide with the passage of a tropical wave (former Invest 91L) currently located near the 40W.

Under this evolving pattern, the highest chance of showers and thunderstorms is expected on Wednesday and Thursday, with a transition on Friday and into the weekend. Having said this, the intensity and coverage of showers and thunderstorms are expected to decrease by the end of the workweek, resulting in a more seasonal pattern with afternoon showers and thunderstorms primarily focused on the western areas of Puerto Rico. As a result, the flooding risk remains elevated throughout the forecast period, decreasing somewhat by the upcoming weekend.

Maximum temperatures will continue to range in the upper 80s to mid 90s with heat indices exceeding 100 degrees F under the prevailing east southeast wind flow. Therefore, the heat risk will remain elevated for much of the forecast cycle. Some haziness is anticipated Wednesday and Thursday.

AVIATION

(06Z TAFS)

Brief reductions in VIS/CIGs due to SHRA/TSRA are possible across JSJ/IST/ISX through this afternoon, resulting in brief MVFR/IFR. Then SHRA/TSRA will spread into the interior and W-PR btwn 07/15- 23z, affecting JPS/JBQ. Expect calm to light/VRB winds thru 07/13z. Aft 07/13Z, winds will return from the ESE at 10-15 kt but locally higher in and near TSRA. Streamer downwind from the USVI or El Yunque could also affect ISX/IST and TJSJ, respectively.

MARINE

A surface high pressure across the Central Atlantic will promote moderate to locally fresh easterly winds, resulting in moderate chops through the middle of the week. An easterly perturbation will continue to promote showers and thunderstorms across the regional waters today and tomorrow. Then, a tropical wave is expected to move near the islands around Wednesday, increasing local winds and potentially triggering showers and thunderstorms again.

BEACH FORECAST

A low risk of rip currents will continue to prevail across all shorelines. Nevertheless, isolated stronger rip currents may occur in the vicinity of groins, jetties, reefs, and piers. Beachgoers must also stay aware of the weather conditions across the area, particularly in the afternoons and evenings, due to thunderstorm activity that may approach the surf zone. Beachgoers must leave the water and seek shelter if thunderstorms are close by.

SJU WATCHES/WARNINGS/ADVISORIES

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