Thursday, July29, 2021
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Marine Weather and Tides
Arroyo, PR

Version 3.4
3/30/2021 -- ANZ330 has been split into ANZ331 and ANZ332. Click EDIT in Marine Forecast and select your new zone.
1/26/2021 -- The West Coast Satellite images havd been updated. They now use GEOS-17.
1/1/2021 -- The 7 day forecast are now working well. Thank you NOAA for your support.

Sunrise 5:27AMSunset 6:06PM Thursday July 29, 2021 3:55 PM CST (21:55 UTC) Moonrise 12:00AMMoonset 11:18AM Illumination 70% Phase: Waning Gibbous; Moon at 20 days in cycle
NOTE: Some of the data on this page has not been verified and should be used with that in mind. It may and occasionally will, be wrong. The tide reports are by xtide and are NOT FOR NAVIGATION.
Marine Forecasts
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7 Day Forecast for Marine Location Near Arroyo, PR
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location: -34.81, -58.22     debug

Area Discussion for - San Juan, PR
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Area Forecast Discussion National Weather Service San Juan PR 446 PM AST Thu Jul 29 2021


A TUTT Low will continue to enhance showers and thunderstorms, especially across the local waters tonight. A mid-level ridge will displace this TUTT-low early Friday, and it will hold aloft through early next week. A wind surge associated with Saturday's tropical wave will reach the islands tomorrow. The bulk of Saturday's wave moisture will remain well south across the Caribbean Waters, while PR/USVI can expect a drier air mass with Saharan Dust Particles.

SHORT TERM. Tonight through Sunday .

A TUTT-low will enhance an easterly perturbation across the islands tonight. As a result, showers and thunderstorms will affect portions of the local waters, the U.S. Virgin Islands, and PR's eastern, northern, and southern sections. Periods of moderate to heavy showers could produce ponding of water in roads and low- lying areas.

Moisture will slowly erode tomorrow ahead of the next tropical wave, which should arrive first as a wind surge around Friday afternoon, then a drier air mass will reach by late tonight into the weekend. This dry air mass will be accompanied by African Dust particulate, while the wave's bulk of moisture should remain well south of the islands across the Caribbean Sea. A mid-level ridge is another factor that will limit widespread shower activity during the weekend, and most of the action will be confined across the western sections of the islands and downwind from the Yunque.

LONG TERM. Sunday through Friday . from previous discussion .

A drier air mass with saharan Dust particles will continue to move over the forecast area on Sunday. As a result, fair weather conditions with hazy skies are expected to prevail for the first day of the long term forecast (Sunday). Tuesday now looks like it has better potential for shower development. First, the surface high pressure across the central Atlantic is expected to induce a southeasterly component in the winds over the forecast area. As a result, this wind flow will drag some patches of moisture with precipitable water above normal. Meanwhile, at the upper levels, the ECMWF and GFS model guidance is suggesting a Tropical Upper Tropospheric Trough (TUTT) moving westward into the local area, which will help increase thunderstorm potential. At this time, the models kind of agree in the timing of the most unstable conditions over the region. That said, expect morning showers over the eastern sections of Puerto Rico and the U.S. Virgin Islands. Then, in the afternoon hours, Galvez- Davison index suggest the possibility of scattered thunderstorms across northwestern quadrant of Puerto Rico. Confidence in the forecast is moderate, but still a few days to follow the dynamics in the upper levels and the moisture content.

For Wednesday onward, a rainy pattern is expected. On Wednesday, several patches of moisture are expected to filter into the region. The combination of the available moisture with the local effects and the upper level dynamics, will result in afternoon convection over the western sections of Puerto Rico, while isolated to scattered showers are expected elsewhere. On Thursday morning, a slot of dry air will move over the area, limiting the shower activity, but after that, in afternoon hours, a tropical wave is expected to increase the potential for shower activity once again through Friday. As a result, shower development is expected, mainly over the northwestern quadrant of Puerto Rico and the San Juan metro area each day.


Mostly VFR conds will continue to prevail at all TAF sites with SHRA/VCTS expected across NW-PR and portions of the San Juan Metro Area through 29/22z. Therefore, SHRA/VCTS in and around JBQ/JSJ will remain possible this afternoon. Winds will be from the east to southeast up to 20 kts with higher gusts and sea breeze variations, becoming at 10 knots or less overnight.


Across the regional waters, choppy marine conditions will prevail over the next several days due to winds up to 20 kts. Seas of up to 5 feet will prevail across the regional waters for the next several days. For beachgoers, there is a moderate risk of rip currents for the northern and southeastern beaches of Puerto Rico as well most of the beaches of Culebra, Vieques and Saint Croix.

Thunderstorms will develop across the local waters, especially over the Caribbean Offshore waters overnight. Mariners should exercise caution.

PRELIMINARY POINT TEMPS/POPS. SJU 78 88 79 88 / 50 30 20 10 STT 79 89 80 89 / 40 20 20 20



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