Puerto Rico Caribbean Waters from 10nm to 17N Marine Forecast
|Rest Of Today...South Winds 5 To 10 Knots. Seas Around 2 Feet Or Less. Dominant Period 11 Seconds. Isolated Showers.|
|Tonight...West Winds 5 To 10 Knots, Becoming Northwest After Midnight. Seas Around 2 Feet Or Less. Dominant Period 11 Seconds. Isolated Showers.|
|Thursday...West Winds 5 To 10 Knots. Seas 1 To 3 Feet. Dominant Period 11 Seconds. Isolated Showers.|
|Thursday Night...North Winds 10 To 15 Knots. Gusts Up To 25 Knots In The Evening. Seas 3 To 5 Feet With Occasional Seas Up To 6 Feet. Dominant Period 11 Seconds. Scattered Showers.|
|Friday...Northeast 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 2 To 4 Feet With Occasional Seas Around 5 Feet. Dominant Period 12 Seconds. Isolated Showers.|
|Sunday...Southeast 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
859pm AST Monday September 25 2023
The 26/00z SJU upper air sounding indicated 1.84 inches of precipitable water and moderate low-level trades between 14 and 18 knots. This helped to trigger a late streamer from Culebra into eastern PR, causing scattered showers to move further inland into portions of Caguas, Cayey, San Lorenzo, and Cidra during the evening hours. Meanwhile, advective showers were increasing across the Atlantic coastal waters of PR, and a strong thunderstorm complex is lingering over the Mona Passage, where a Marine Weather Statement is in effect through 10 PM. In the meantime, an area of drier air and a developing TUTT low just north of the Leeward Islands should promote fair weather conditions overnight, however, trade wind showers moving at times across portions of the USVI and eastern PR cannot be ruled out.
No change from previous discussion. Light to moderate east to northeast trades expected through the end of the week. NE swell from TC Phillipe will cause life- threatening rip currents along the eastern and northern beaches of PR, Culebra, and St. Croix on Wednesday and Thursday.
/issued 407pm AST Monday September 25 2023/
SYNOPSIS... Winds will shift from the northeast this week as Tropical Storm Phillipe moves far away from the region. Moisture will decrease a little tomorrow, but seasonal afternoon showers are expected for the interior and western Puerto Rico. Marine conditions could deteriorate a little by the later part of the week across the offshore Atlantic waters.
SHORT TERM...Tonight through Wednesday... Intense heat was again observed along the local islands, with heat indices surpassing the heat warning criteria (112 degrees) along northern and western Puerto Rico, Vieques, Culebra and St. Croix. Other stations in the eastern interior, east, south, St. Thomas and St. John also experienced values above 108 degrees, were heat advisories were in effect. This strong heating combined with the above normal moisture crossing the islands to generate strong showers and thunderstorms. The activity was observed in a line from St. Thomas into Culebra, then into eastern Puerto Rico, and additional activity from the east interior toward western Puerto Rico. The highest accumulations were for San Sebastian, Anasco and San German, with over 1.5 inches of rain collected.
The activity should taper off by sunset, but some pesky showers may linger into western Puerto Rico a little later than this. Satellite imagery shows that some small patches of clouds will continue to move in tonight, triggering some showers along eastern Puerto Rico and over the U.S. Virgin Islands. Then, early tomorrow, a small pocket of drier air, with precipitable water values dropping to near 1.6 inches, and a trade wind cap inversion around 900 mb. This all translate into less rain coverage over the area, although it will not be completely dry. The winds will shift from the northeast through mid-week due to the external circulation of Tropical Storm Phillipe, which will stay well away from the islands. On Wednesday, additional patches of moisture will reach the islands, increasing the potential for showers and the area. Rainfall activity should be stronger for the interior and southwest each day, with an enhanced risk for urban and small stream flooding in these areas.
In terms of temperatures, winds from the northeast could bring some slight relief from the scorching heat, but 925mb temperatures will remain above normal, so some places will still experience heat indices above 108 degrees. Users are advised to stay hydrated and protected from the sun, mainly from 10 to 5pm AST.
A mid to upper-level trough and an induced surface trough will continue moving into the Central Caribbean Sea on Thursday. This weather pattern means to Puerto Rico and the U.S. Virgin Islands that we can expect typical conditions but with a higher frequency of passing showers across the early morning hours across the local waters and windward sections, followed by afternoon convection across West PR and downwind from the Islands.
A mid-level high pressure system will develop over the Northeast Caribbean area on Friday. This system might strengthen trade wind inversion and lead to subsidence in the upper atmosphere. Despite this, the northeast winds, which are moving over warmer waters than usual, might cause isolated rain showers in the regional waters and windward areas of Puerto Rico and the U.S. Virgin Islands early in the morning. During the afternoon, there could be one or two intense thunderstorms due to local effects and excessive heating across West PR. By the weekend, a region with dry air could settle over the islands, but we cannot rule out the typical rain pattern (expressed above).
Once again, the model guidance tends to develop a cyclone by the end of the forecast cycle (around Monday or early next week). High uncertainty with the track and intensity is present, which is typical at this time of the year due to the meteorological guidances' climatological aspects, among other factors. Nonetheless, we recommend that locals stay updated by checking in with our Weather Forecast Office and the National Hurricane Center, given that the Hurricane Season runs until November 30th.
Current model guidance suggests northeasterly winds Thursday through Friday and dying out Saturday onward. Maximum temperatures will range in the upper 80s and low 90s across most urban areas. Combining the available moisture and the air temperature could extend the hot spell across these areas through the Long Term period.
AVIATION... TSRA/SHRA (rain showers) could result in brief MVFR (Marginal Visual Flight Rules) conditions, mainly across all PR terminals through 24/22Z, followed by VCSH after 24/22Z for TJSJ and USVI terminals. Easterly winds at 10-15 knots with higher gusts and sea breeze variations, becoming light and variable after 24/22Z. Higher wind gusts likely near TSRA/SHRA.
Seas will remain at 3 to 5 feet along the local waters. Marine conditions will remain similar through mid-week, then seas will increase to around 6 feet for the Atlantic waters throughout the end of the week. The risk of rip currents is moderate for the northern coast of PR, Vieques, Culebra, and for all of the U.S. Virgin Islands.
.SJU WATCHES/WARNINGS/ADVISORIES... PR...None. VI...None. AM...None.