Marine Weather Net

Port Mansfield, TX to the Rio Grande River 20 - 60 NM Marine Forecast


10 - 15


15 - 20


15 - 20


10 - 15

The Marine Weather Forecast In Detail:
GMZ170 Forecast Issued: 939 AM CDT Sun Oct 25 2020

Rest Of Today...Southeast Winds 10 To 15 Knots. Seas 2 To 4 Feet.
Tonight...Southeast Winds 15 To 20 Knots. Seas 3 To 5 Feet.
Monday...Southeast Winds 15 To 20 Knots Diminishing To 10 To 15 Knots In The Afternoon. Seas 3 To 5 Feet.
Monday Night...East Winds 10 To 15 Knots. Seas 3 To 5 Feet. Slight Chance Of Showers After Midnight.
Tuesday...East Winds 10 To 15 Knots Shifting Northeast In The Afternoon. Seas 3 To 5 Feet. Chance Of Showers.
Tuesday Night...North Winds 10 To 15 Knots Increasing To 15 To 20 Knots After Midnight. Seas 5 To 7 Feet With Occasional Seas Up To 8 Feet. Chance Of Showers.
Wednesday...Northwest Winds 15 To 20 Knots. Seas 6 To 9 Feet With Occasional Seas Up To 10 Feet. Chance Of Showers.
Wednesday Night...Northwest Winds 15 To 20 Knots Becoming North 10 To 15 Knots After Midnight. Seas 7 To 10 Feet With Occasional Seas Up To 12 Feet.
Thursday...Northwest Winds 15 To 20 Knots Diminishing To 10 To 15 Knots In The Afternoon. Seas 5 To 7 Feet With Occasional Seas Up To 8 Feet.
Thursday Night...North Winds 10 To 15 Knots Increasing To 15 To 20 Knots After Midnight. Seas 5 To 7 Feet With Occasional Seas Up To 8 Feet.
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Synopsis for Baffin Bay to Rio Grande out 60 nm: GMZ100
939 AM CDT Sun Oct 25 2020

A tightening pressure gradient will lead to strengthening southeast winds over the coastal waters. Seas will gradually build in response through Monday night. Small craft should continue to exercise caution due to stronger winds and building seas. Winds will shift around to northerly flow on Tuesday as a cold front moves through the area. Moderate to strong northerly winds will follow this front, resulting in a prolonged period of hazardous marine conditions for much of the coastal waters.
Area Forecast Discussion
...UPDATED National Weather Service Brownsville TX
1232pm CDT Sunday Oct 25 2020

AVIATION...Ceilings are lifting to VFR this morning as satellite shows erosion of the coastal low cloud bank. Conditions should be mainly VFR today with moderate to breezy southeast winds along the coast. Low clouds will thicken again tonight with some lower ceilings. A few hours of MVFR (Marginal Visual Flight Rules) ceilings will be possible from late this evening through early Monday morning.

Short Term - Today Through Monday
Overhead high pressure will dominate, slowly shifting east ahead of an upper ridge through the short term. Lower pressure will develop upstream over North Central Mexico, supporting a tighter gradient and moderate to breezy (along the coast) southeast winds. Temps will be above average under a mix of clouds and sun. No significant rainfall is forecast. Tides and residuals are coming down a bit, with the next high tide on Monday at around 2:12 AM. Beach runup should be less today, but there could be very isolated minor beach flooding still Sunday night into early Monday morning around high tide.

Long Term - Monday Night through Saturday
To say the long-term forecast is complicated is a major understatement. Before reading on, just know that there is major forecast uncertainty, especially Tuesday through Thursday.

As mentioned in previous AFDs, models are in agreement that a vigorous mid-level cut-off low will dig southward over the Intermountain West, possibly digging as far south as extreme northwest Mexico by early Tuesday morning.

The long-term forecast really depends on multiple factors: 1.) Exactly how far south the mid-level low will dig. 2.) How deep/strong the mid-level low will be. 3.) How strong the subtropical ridging will be over the Southeast CONUS. 4.) What TS Zeta will do in the Gulf of Mexico.

Overall, and in a nutshell, didn't make too many changes to the previous forecast. Will continue to lean more towards the NAM solution, with some modifications, which brings the front through Deep South Texas late Monday night or early-mid Tuesday morning. Still not confident enough to go as low with the temperatures as it is suggesting, so kept temperatures about 2-5 degrees warmer on Tuesday. Assuming this solution does verify, there will be a pretty tight temperature gradient west-to-east on Tuesday, with highs in the upper 50s/lower 60s west and mid-upper 60s/lower 70s east. Reasoning for the warm temperatures near the coast is because of the higher dewpoints, caused by the presence of Tropical Storm (forecast to become a hurricane) Zeta, helping keep temperatures on the warmer side. Zeta is forecast to make landfall sometime on Wednesday along the LA/MS coast. Only impacts to Deep South Texas at this time will hazardous marine conditions and minor/moderate coastal flooding at South Padre Island. Better details on this in later updates. Cold Air Advection is expected to continue into Wednesday, with breezy north/northwest winds, though more sun will cause temperatures to warm up into the mid-upper 60s and lower 70s.

As the aforementioned upper-low lifts northeastward on Thursday, elongated subtropical ridging will begin to build back over Southern Texas, with very dry air continuing to filter in both at the mid-levels and lower-levels of the atmosphere. This will result in dry weather, with very comfortable day-time temperatures and chilly night-time temperatures through the remainder of the week and into the weekend. Temperatures are expected to be near or slightly below seasonal average Thursday-Saturday.

Marine - Now through Monday
The surface pressure gradient will tighten today, resulting in stronger, moderate to fresh southeast winds this afternoon. Small craft should exercise caution on the Laguna and nearshore waters. Persistent moderate to fresh southeast winds will then nudge seas higher into moderate territory through Monday.

Monday night through Saturday: A moderate to strong cold front is forecast to push over the coastal waters Tuesday morning or early afternoon. A tight pressure gradient ahead of the front will cause breezy southeast winds, likely causing SCEC conditions (Small Craft Should Exercise Caution) Monday night and into Tuesday morning. There is still lots of uncertainty with the cold front, especially with regards to timing. Regardless of timing, SCEC and/or SCA (Small Craft Advisory) conditions will likely follow behind the front, both on the bay and Gulf waters. In addition, Tropical Storm Zeta will track northward across the central Gulf of Mexico during the day on Wednesday, building swell on the Gulf during through the day. Seas are expected to build to near 10 feet across the offshore Gulf waters Wednesday evening/night, keeping conditions very unfavorable for small craft. Winds and seas will gradually decrease on Thursday, but both will remain very agitated/rough through the end of the week. Marine conditions finally become favorable by Saturday.

NOAA Brownsville TX Office: Watches - Warnings - Advisories
TX...None. GM...None.