Marine Weather and Tide Forecast for South Haven, MI

DISCUSSION
Issued at 412 AM EDT Sat Apr 18 2026

- Cooler For A Few Days, Then Warming Back Up Mid-Late Week

Welcome relief from the recent rainy pattern as a progressive synoptic trough over Canada and the northern CONUS sweeps a cold front through this morning, with 850 mb temperatures expected to cool 20 C in 24 hours, between early this morning and early Sunday morning. A shortwave digging into the backside of the trough over Michigan on Sunday may support some wet snow showers. The coldest air, down to -10 C at 850 per the ECMWF, will be in place underneath a center of high pressure Sunday night. As a result, lows in the 20s are favored Sunday night / Monday morning. Note, we will begin the frost/freeze headlines for Muskegon, Kent, Montcalm, Gratiot, and south. High temperatures Sunday and Monday are favored to be in the 40s, about 10-15 degrees below normal.

Ensembles do have pretty good agreement on temperatures rebounding into the 60s Tuesday as the synoptic wave pattern progresses eastward and southwesterly flow brings warmer air back. Most ensemble members have temperatures peaking for the week on Thursday with highs well into the 70s. Instability may build again Thursday and Friday with a chance of thunderstorms, followed by a a chance of a cooling trend for the weekend.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/
Issued at 744 AM EDT Sat Apr 18 2026

MVFR to IFR ceilings this morning with rain in the vicinity of a passing cold front. The front, which can be seen via a thin line of showers from RQB to GRR to west of AZO at 1145 Z, is moving east with time. Ahead of the front, winds are from the southwest, and then winds shift to be from west-northwest after it passes.
Winds will gust around 20-30 knots much of the day. Medium confidence that ceilings scatter out to VFR by afternoon, but there could be some lingering cumulus at or below 3,000 feet.

MARINE
Issued at 412 AM EDT Sat Apr 18 2026

Colder air flowing in behind a cold front with west winds gusting 25-30 knots will build 3-6 ft waves today into Sunday morning.
Lower waves are expected Sunday night into Monday with lighter winds as high pressure moves over the region.

HYDROLOGY
Issued at 744 AM EDT Sat Apr 18 2026

Major flooding continues on the Muskegon River. The good news is that the river at most locations will be cresting soon (Upstream areas of the river including Evart crested earlier Friday). It will likely take until late next week for all locations to come under flood stage, so the recovery process will be slow.
Meanwhile, water levels continue to rise on the Grand River, and confidence is increasing that this will end up being another minor flood event, slightly higher and worse than the one that happened earlier this month, but not a record flood at any locations.
However, some of the lowest and easily flooded locations on the river like Comstock Park and Robinson Township will have moderate flooding. Comstock Park may stay just under Major.

The final round of substantial precipitation fell last night, and was roughly in line with what was forecast, between 0.25 and 0.75 inches for most areas. As such, only minor adjustments should be needed to the going forecasts.

GRR WATCHES/WARNINGS/ADVISORIES
MI...None.
MARINE...Small Craft Advisory until 8 AM EDT Sunday for LMZ844>849.