Thursday, January21, 2021
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Marine Weather and Tides
Arroyo, PR

Version 3.4
NOTICE
8/26/2020 The 7 day forecast is taking about 5 seconds to load but it will eventually load. NOAA is still working on it.
8/18/2020 NOAA continues to have trouble. Wind guest will occasionally be left off graphs. I am working with NOAA to resolve the issue.
12/16/2019 NOAA is having trouble with requests that include wind gusts. I am posting graphs without wind gusts until it gets fixed.
10/9/2019 Updated the Marine Zones.
9/4/2019 Fixed the weather maps due to NOAA moving them.
7/25/2019 New feature in the Airports section gives a link to 5 minute updates for data reports.

Sunrise 6:03AMSunset 5:40PM Thursday January 21, 2021 9:11 PM CST (03:11 UTC) Moonrise 2:00PMMoonset 12:35AM Illumination 63% Phase: Waxing Gibbous; Moon at 9 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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FXCA62 TJSJ 220158 AFDSJU

Area Forecast Discussion National Weather Service San Juan PR 958 PM AST Thu Jan 21 2021

UPDATE. Afternoon showers lingered once again into the evening hours over mainland Puerto Rico, but the shower activity today was over southwestern PR, as steering winds are from the east to northeast. Rain gages reported between a quarter to three quarters of an inch of rain with the most persistent showers. Additional showers were observed over sections of the eastern interior this afternoon. For the rest of tonight, light northeast trades could bring the occasional passing shower over the eastern and northern sections of the islands. However, no significant rainfall amounts are anticipated.

AVIATION. Mainly VFR conditions are expected to prevail across all terminals during the next 24 hours. The 22/00z TJSJ sounding indicated east winds up to 12 kts below FL050.

MARINE. Seas will continue to range in general between 3-5 feet across the Atlantic waters and passages, while seas at less than 4 feet are expected across the southern waters of the islands. Light winds up to 10 kt are expected to continue through the overnight hours. A small northerly swell will fill later on Friday afternoon

PREV DISCUSSION. /issued 359 PM AST Thu Jan 21 2021/

SYNOPSIS . Although patches of moisture may bring showers from time to time across the islands, significant rainfall is not anticipated through the next few days. A cold front may approach the islands by Tuesday next week. Generally tranquil marine conditions with light to moderate winds are expected to prevail through early Friday.

SHORT TERM . Tonight through Saturday

A polar trough continues to move across the north Atlantic Ocean, which has resulted in a lighter northeast flow across the islands, as well as in a weaker trade wind cap over the region. As a result, showers were able to develop in the form of streamers from the U.S. Virgin Islands, Vieques, Culebra, and near El Yunque. Additional activity was observed over western Puerto Rico, with moderate rainfall accumulation detected by the Doppler radar. As the Sun sets, these showers will lose fuel and should begin to weaken and dissipate through the evening hours.

For the rest of the short-term forecast period, the polar trough will begin to move away into the eastern Atlantic, while a mid- level high pressure builds over the northwestern Caribbean Sea. This will act to restrengthen the trade wind cap over the islands. Additionally, moisture content will remain limited, with only occasional pockets of clouds moving across the region. Therefore, some advective showers will be possible early in the day and in the overnight hours over eastern Puerto Rico and the U.S. Virgin Islands. In the afternoon, scattered showers may develop over the interior and western Puerto Rico, aided by diurnal heating and sea breeze convergence. Rainfall accumulation, are not expected to be significant, though, due to the lack of dynamic support in the mid and upper levels.

LONG TERM . Sunday through Thursday . /from prev discussion/

Model guidance suggests that mainly fair and stable weather conditions will dominate the region through the long-term forecast period. However, patches of low- level moisture embedded in the trade winds will bring brief periods of cloudiness and isolated to scattered shower activity from time-to-time. A slight enhancement of moisture along with increased cloudiness and shower activity may be expected between Tuesday and Thursday as the remnants of an old frontal boundary move into the forecast area. However, model guidance does not suggest significant moisture content, with model- estimated precipitable water vapor briefly fluctuating from less than an inch on Monday to 1.30 inches by Thursday afternoon. Mid-level ridging will promote subsidence and drier air aloft, conditions that will limit any chance for organized convective development, even with the highest available moisture. That said, significant wetting rains are not anticipated, which will enhance further dryness of soil and fuels, while promoting favorable fire weather conditions.

AVIATION . VFR SCT lyrs nr FL030. FL050 . SKC ABV. Mostly Isold SHRA ovr coastAl waters btw Eastern PR and USVI. No sig operational wx impacts durg prd. Sfc wnds fm E-NE 5 to 15 mph except for sea breeze variations and isold wnd gusts . bcmg lgt/vrb aft 21/23Z.

MARINE . Tranquil marine conditions and light winds are expected to continue through the end of the week. Then, by late Friday and early Saturday, a small northerly swell is expected to create choppy seas over the Atlantic waters, with wave height up to 6 feet.

For the beaches, there is a moderate rip current risk for the north, east, and southeast coast of Puerto Rico, as well as for Vieques and Culebra. In the U.S. Virgin Islands, a moderate rip current risk exist for the northwest coast of St. Thomas, south of St. John, and eastern St. Croix.

PRELIMINARY POINT TEMPS/POPS. SJU 73 84 72 83 / 20 20 20 20 STT 73 85 73 83 / 30 30 30 20

SJU WATCHES/WARNINGS/ADVISORIES. PR . None. VI . None. AM . None.

UPDATE . DSR SHORT TERM . ERG PUBLIC DESK . LIS


Weather Reporting Stations
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Airport Reports
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Tide / Current Tables for
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Weather Map
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NOTE: East coast views moved to GEOS-16. They are experimental and not well supported by NOAA so they may not be correct so be warned. This change required redoing a large amount of the GOES code. If the image you are expecting is not showing, please let me know. You may need to use the EDIT function to update your location.
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The information on this web site has not been checked for accuracy. It is for entertainment purposes only and should be independently verified before using for any other reason. There are five sources. 1) Documents and manuals from a variety of sources. These have not been checked for accuracy and in many cases have not even been read by anyone associated with L-36.com. I have no idea of they are useful or accurate, I leave that to the reader. 2) Articles others have written and submitted. If you have questions on these, please contact the author. 3) Articles that represent my personal opinions. These are intended to promote thought and for entertainment. These are not intended to be fact, they are my opinions. 4) Small programs that generate result presented on a web page. Like any computer program, these may and in some cases do have errors. Almost all of these also make simplifying assumptions so they are not totally accurate even if there are no errors. Please verify all results. 5) Weather information is from numerous of sources and is presented automatically. It is not checked for accuracy either by anyone at L-36.com or by the source which is typically the US Government. See the NOAA web site for their disclaimer. Finally, tide and current data on this site is from 2007 and 2008 data bases, which may contain even older data. Changes in harbors due to building or dredging change tides and currents and for that reason many of the locations presented are no longer supported by newer data bases. For example, there is very little tidal current data in newer data bases so current data is likely wrong to some extent. This data is NOT FOR NAVIGATION. See the XTide disclaimer for details. In addition, tide and current are influenced by storms, river flow, and other factors beyond the ability of any predictive program.