Southern US Virgin Islands, Vieques and Eastern Puerto Rico out 10nm Marine Forecast
| Rest Of Today...Southwest Winds 5 To 10 Knots. Seas 1 To 3 Feet. Dominant Period 11 Seconds. Isolated Showers. |
| Tonight...West Winds 5 To 10 Knots. Seas 1 To 3 Feet. Dominant Period 10 Seconds. Isolated Showers. |
| Thursday...West Winds 5 To 10 Knots. Seas 2 To 4 Feet With Occasional Seas Around 5 Feet. Dominant Period 10 Seconds. Numerous Showers. |
| Thursday Night...North Winds 10 To 15 Knots. Seas 4 To 6 Feet With Occasional Seas Up To 8 Feet. Dominant Period 11 Seconds. Scattered Showers. |
| Friday...North Winds 10 To 15 Knots With Gusts Up To 25 Knots. Seas 3 To 5 Feet With Occasional Seas Up To 6 Feet. Dominant Period 11 Seconds. Isolated Showers. |
| Saturday...Southeast Winds 5 To 10 Knots. Seas 3 To 5 Feet With Occasional Seas Up To 6 Feet. Dominant Period 12 Seconds. Isolated Showers. |
| Sunday...South Winds 5 To 10 Knots, Becoming East. Seas 3 To 5 Feet With Occasional Seas Up To 6 Feet. Dominant Period 12 Seconds. |
| Area Forecast Discussion National Weather Service San Juan PR 103pm AST Sunday July 19 2026 .Short Term(This evening through Tuesday)... Issued at 103pm AST Sunday July 19 2026 Local weather stations across the islands reported maximum temperatures in the 90s at most urban and coastal locations. Peak heat index values ranged from 100°F to 107°F. Winds were generally from the east at 15 to 25 mph, with higher gusts at times. Although skies remained mostly clear across much of the region, clouds began to develop over the interior and western Puerto Rico due to orographic and local effects, as well as sea-breeze convergence. Also, a streamer was observed forming over and downwind from St Croix. Although a tropical wave will move well south of the islands, its trailing moisture will interact with local topography, daytime heating, and sea breeze convergence, resulting in afternoon showers across portions of Puerto Rico. A streamer will possibly develop downwind of the U.S. Virgin Islands, remaining primarily over the local waters. At the surface, high pressure over the central Atlantic will maintain breezy easterly trade winds through the forecast period. Meanwhile, hot conditions will persist across most urban and coastal areas of Puerto Rico and the U.S. Virgin Islands, with a limited risk of excessive heat through late this afternoon. A Saharan Air Layer (SAL) will spread across the region through early this week, resulting in hazy skies, reduced air quality, and warmer overnight temperatures that may increase heat stress. At the same time, the trailing moisture associated with today's tropical wave will move across the area on Monday, increasing low- level moisture and potentially elevating the risk of excessive heat from mid-morning through the afternoon due to higher heat index values. This additional moisture will also support scattered showers capable of producing moderate to locally heavy rainfall, particularly where local effects enhance convection. However, a mid- to upper-level ridge will continue to promote subsidence aloft and maintain a trade wind inversion, limiting the vertical extent of convection despite increased moisture. Model guidance suggests an induced trade wind perturbation will move across the region on Tuesday. Some solutions, including the deterministic GFS, indicate moisture deepening to around 600 mb as the perturbation weakens the trade wind inversion associated with the mid-level ridge. This feature, combined with daytime heating and local island effects, will provide the greatest potential for afternoon thunderstorm development, especially across the interior and western portions of Puerto Rico. One or two localized, stronger thunderstorms could produce ponding across poorly drained areas and isolated urban and small-stream flooding. Long Term Issued at 452am AST Sunday July 19 2026 During the beginning of the long-term period, the primary weather feature will continue to be an upper-level low inducing a surface trough northeast of the region. This pattern will weaken the Atlantic high pressure system, promoting lighter winds across the islands. The latest guidance suggests that environmental conditions will be marginally favorable for convective activity. Winds will become lighter from the east-northeast. At 500 mb, temperatures are forecast to cool from above-normal values to near-seasonal levels, around -6C to -7C. In addition, lower 250 mb heights, near- seasonal mid-level relative humidity, and precipitable water (PWAT) values remaining around 1.7 to 1.9 inches will support a more favorable environment for shower and thunderstorm development. A limited flood risk is highlighted across west- central and western Puerto Rico due to the potential for ponding of water on roads and in poorly drained areas, along with a low chance of urban and small- stream flooding. Additionally, on Wednesday, the combination of light southeasterly flow, seasonal moisture, and 925 mb temperatures around two standard deviations above normal is expected to result in the warmest day of the week. Heat index values will likely reach hazardous levels each afternoon, especially across urban and coastal locations. A significant heat risk is currently highlighted for Wednesday. Heat products will likely need to be issued. By Thursday and through the remainder of the forecast period, slightly drier air is expected to filter into the region, with PWAT (Precipitable Water) values fluctuating between seasonal and below-normal levels, resulting in more limited shower activity. Winds are forecast to strengthen once again, becoming breezy to locally windy through the weekend. The easterly steering flow will continue to favor passing showers across windward areas during the nighttime and morning hours, followed by afternoon showers over western Puerto Rico driven by local effects and available moisture. The flood risk is expected to remain low, although a few isolated thunderstorms will remain possible each afternoon across western Puerto Rico. In terms of heat, warm to hot conditions are likely to persist most days. An elevated heat risk is currently in place for Thursday, while a limited heat risk is expected on Friday. Continue to monitor the forecast for updates. Residents and visitors are encouraged to continue practicing heat safety measures to reduce the risk of heat- related illnesses. Marine Issued at 103pm AST Sunday July 19 2026 A surface high pressure over the central Atlantic interacting with the Panama–Colombia Low will maintain moderate to fresh easterly winds and moderate to locally choppy seas through much of the forecast period. A tropical wave will remain well south of Puerto Rico and the U.S. Virgin Islands as it moves westward across the southern Caribbean through Monday. Meanwhile, a dense Saharan Air Layer will move over the region from the east tonight through tomorrow, Monday, leading to hazy skies, reduced air quality, and locally reduced visibilities. Beach Forecast Issued at 103pm AST Sunday July 19 2026 Increasing easterly trade winds will enhance wave-breaking action along many beaches of Puerto Rico and the U.S. Virgin Islands through much of the week, resulting in a moderate risk of life- threatening rip currents across numerous surf zones. The moderate risk is expected to persist throughout much of the week for many north-, east-, and south-facing beaches, although localized day- to-day variations are possible. Beachgoers should swim near lifeguards whenever possible, heed beach warning flags, and never swim alone. A limited-to-local elevated risk of excessive heat is also expected at many local beaches through the first half of the week, particularly during the late morning and afternoon hours. Stay well hydrated, take frequent breaks in the shade, and use sunscreen to reduce the risk of heat-related illnesses. Fire Weather Issued at 103pm AST Sunday July 19 2026 A Fire Danger Statement (RFD) remains in effect for the local fire weather zones. Observations continue to support RFD conditions across the southern half of PR and the USVI. At the same time, critically dry fuels and persistent soil moisture deficits persist across portions of the islands, with KBDI values remaining above critical thresholds. Multiple fire incidents have already been reported across PR today, underscoring the elevated fire danger. Combined with breezy trade winds, any new fires that develop could spread rapidly through dry vegetation, particularly across PR's southern coastal plains. Residents and visitors are urged to avoid outdoor burning and exercise extreme caution with open flames, discarded cigarettes, or any activity capable of producing sparks. .SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None. |
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