Marine Weather and Tide Forecast for Port Isabel, TX

SHORT TERM
(Tonight through Sunday night)
Issued at 232 PM CST Sat Dec 7 2024

As the coastal trough continues to move towards the north and away from Deep South Texas and the Rio Grande Valley, the low-level clouds over the region are expected to lessen through the short-term forecast period. Starting off with the temperatures for the short- term forecast period, the low temperatures for tonight are expected to be mostly in the low to mid 50s, however parts of the Upper Valley could get into the upper 40s tonight. Moving into Sunday, with the low-level clouds expected to lessen and even clear in some parts of the region, the high temperatures could be in the range of the mid and upper 60s to low 70s depending on the timing of when the low-level clouds lessen or clear. If the low-level clouds persist longer than what is currently forecasted then the high temperatures could be much cooler than what is currently forecasted. To close out the section on temperatures, low temperatures for Sunday night are expected to be mostly in the low to mid 60s, however once again parts of the Upper Valley could be colder than the rest of the region with low temperatures in the upper 50s.

With the coastal trough pulling away, chances of rain are also expected to decrease as well even though there is still plenty of low-level moisture. However an rogue shower or two is still possible tonight, but by tomorrow expect mostly rain-free conditions for the rest of the short-term forecast period.

LONG TERM
(Monday through next Saturday)
Issued at 232 PM CST Sat Dec 7 2024

Key Messages:

- Moderately strong cold front next Tuesday - Much cooler Wednesday through Thursday morning.
- Gale conditions over the coastal waters possible Tuesday night

Emphasis and the continued forecast challenge in the long term is Tuesday's cold front and temperatures expected Wednesday and Thursday especially low temperatures for the respective days.

Before Tuesday's cold front temperatures warm up considerably as surface winds turn south and possibly gain a slight southwest downslope component with a shortwave trough crossing the Sierra Madre Oriental. 85H temps approach 19-20C which will relate to mid 80s across a large portion of the RGV especially as low clouds clear for the afternoon. The GFS even shows McAllen reaching 89 degrees so some additional adjustments in the current forecast are likely as we approach next week.

Timing of the frontal passage across the RGV is still showing up for a late morning or early afternoon with cold air advection lagging 2-4 hours in wake of the frontal boundary. Highs on Tuesday still expected to reach into the 70s across the north and likely to tip over 80 degrees in advance of the front for the RGV. There is a slight chance of a shower developing along the immediate front as it crosses the Lower RGV and runs into higher moisture content over the coastal waters.

As for the colder air, latest deterministic and ensemble models remain persistent on the cold air advection (CAA) lowering temperatures significantly for Wednesday morning, Wednesday and Thursday morning. However surface high pressure shifts a bit more quickly to east by Thursday morning with the GFS and ECMWF showing the center of the 1032mb ridge settling over the Southern Gulf States. This should allow for low level east to southeast winds to return late Wednesday night/Thu AM (albeit light) which is likely to cut off the CAA and curtail temperatures from nearing freezing across the northern/western ranchlands or dropping below 40 degrees across the RGV. At this time, the coldest temperatures maybe Wednesday morning with lows in the upper 30s to near 40 north and west and mid to upper 40s for the RGV. Highs Wednesday in the low to mid 60s or approximately 10 degrees below normal.
Thursday morning lows similar to Wednesday AM if not a few degrees warmer than Wednesday AM.

For the end of the week and early next weekend, warmer temperatures with increasing clouds are forecast.

AVIATION
(00Z TAFS)
Issued at 543 PM CST Sat Dec 7 2024

Through 00z Monday....The main weather concerns to aviation ops for the terminals through the 00z TAF cycle is 1) the continuation of MVFR-IFR cigs (low stratus) for most, if not all, of the TAF sites through at least tonight and 2) the potential for rain showers this evening over KMFE.

As of this 00z update, KBRO/KHRL were reporting IFR cigs with cloud bases between 700-800 feet AGL and unrestricted visibilities.
Meanwhile, KMFE was reporting MVFR cigs with ceilings between 1,500-2,000 feet AGL and unrestricted visibilities. According to this morning's 12z KBRO sounding, a strong sfc inversion/cap up to about 960 mb was in place. This was largely due to the copious amounts of low level residual moisture left behind from the recent moderate to at times heavy rainfall episodes from yesterday and even earlier this week. As a strong sfc capping inversion remains in place over the region, mainly IFR cigs are expected to prevail through at least tonight, especially over KBRO/KHRL.
MVFR-IFR cigs are expected through tonight over KMFE due to that area not receiving as much rainfall in previous days. There could be instances of LIFR cigs tonight, especially over KBRO/KHRL as dewpoint depressions narrow further.

As far as precipitation trends through tonight, the latest scans from the mosaic and KBRO WSR-88D Doppler Radar revealed a batch of showers extending from a Jim Hogg County to eastern Starr/Hidalgo County line with additional showers further upstream over Mexico.
These showers are likely to impact KMFE within the next hour and should persist over the next couple of hours or so before coming to an end. Have VCSH and TEMPO groups in place to reflect this potential/risk. There is a chance that these showers make its way into KHRL later on, but confidence at this time is still rather low.
Otherwise, expect for dry conditions to prevail through this evening/tonight.

During the day on Sunday, the clouds look to stick around.
However, there is potential for cigs to show gradual improvements during the day. Have MVFR cigs developing by noon over the TAF sites and prevailing through the remainder of the 00z TAF cycle.

Northwest winds 5-10 kts this evening will trend towards light and variable to calm tonight. During the day on Sunday, winds are expected to develop out of the south at 5-10 kts.

MARINE
Issued at 232 PM CST Sat Dec 7 2024

Tonight through Sunday Night...Light to moderate winds and low to moderate seas are expected to persist through Sunday night resulting in mostly favorable conditions. Some isolated showers are possible mostly over the Offshore Gulf waters.

Monday through Saturday...Fair marine conditions start off the new week with light to moderate southerly winds and low to moderate seas. Marine conditions quickly change Tuesday as a strong cold front surges through late morning or early afternoon Tuesday.
Mariners can expect deteriorating conditions Tuesday afternoon with hazardous conditions Tuesday night and Wednesday. At this time probability of gale conditions Tuesday night have increased and are now as high as 40-60% for the Laguna Madre and 70-80% over the Gulf waters. Rough conditions continue Wednesday with slow improvement Wednesday and Thursday. Fair conditions return to the lower Texas coastal waters Friday and Saturday.

PRELIMINARY POINT TEMPS/POPS
BROWNSVILLE 54 65 62 83 / 20 10 10 0 HARLINGEN 53 65 61 84 / 20 10 10 0 MCALLEN 54 70 61 85 / 30 10 10 0 RIO GRANDE CITY 51 71 61 83 / 40 10 10 0 SOUTH PADRE ISLAND 58 66 66 79 / 20 10 10 0 BAYVIEW/PORT ISABEL 55 65 63 82 / 20 10 10 0

BRO WATCHES/WARNINGS/ADVISORIES
TX...None.
GM...None.