Marine Weather and Tide Forecast for South Haven, MI

DISCUSSION
Issued at 330 AM EDT Wed Apr 30 2025

- Frost and Freeze This morning

Temperatures currently remain in the low 40s with dewpoints in the mid to upper 30s along and south of the I 96 corridor. RH's remain 70 percent or above and winds have just begun to decouple and go calm along the I 94 corridor southward. With dew points above freezing, and winds not calm, it will become difficult for frost to form, and for temperatures to go below freezing. Latest soundings show the low levels continue to mix a little bit down to the surface which is aiding the winds. Patchy frost formation can typically occur once temps get 37 and below.
Another issue is seen in satellite as a cirrus shield overspreads the region from the southwest. The eastern sites south of the I 96 corridor having dewpoints closer to freezing thus have more frost potential.

That said, there remains about 4 hours for temperatures to drop to freezing. Winds should go calm just before sunrise and allow for freezing temperatures through the north and areas of frost elsewhere.

- Showers and Storms Wed Night into early Friday

Echoes of the cold aside, the weak high pressure will give way to a northeastward trough trekking its way through the southern Plains. Gulf moisture will accompany this system bringing a persistent period of rainfall. Latest NAEFS mean PWATS are upwards of 1.25 inches that are +2 to +3 anomalies. The mid to sfc low will intensify as it moves overhead with thunderstorms possible Thursday. These storms will be fueled due to low level shear intensification coupled with warm air advection out ahead of a mid level closed low and a tightening gradient over southern lower Michigan.
Highest rainfall currently is a strip from around Lansing extending to the southwest. However, given convection this could shift and change. Overall QPF will vary from over three quarters of an inch to upwards of 1.5 inches in and around thunderstorms.
Locally higher amounts are possible. Precipitation could linger into the first half of Thursday night on the back side of the low as it exits to the northeast.

- Slightly cooler this weekend with a warm up next week

A deepening trough will move through Friday into Saturday will cooler drier air filtering into the area. Temps will drop with lows near freezing early Saturday morning. Max temps will be around normal but will feel cooler with brisk northwesterly flow.
Patterns begin to diverge so a lack of confidence in long term but overall warmer temperatures will return early next week.

AVIATION /12Z TAFS THROUGH 12Z THURSDAY/
Issued at 747 AM EDT Wed Apr 30 2025

VFR weather is expected today with mid and high clouds spreading in ahead of a low pressure system. Cloud bases today will be at or above 10,000 feet through 00Z. Tonight conditions deteriorate as a warm front nudges our direction from the south producing lower clouds and rain. Ceilings will dip into the MVFR category after 08Z with IFR beginning to show up towards 12Z. Rain will spread in between 03Z and 08Z. Visibilities will largely stay VFR through 12Z on Thursday. Visibilities will begin to drop below VFR levels towards 12Z and beyond. Winds will be easterly at 5 to 10 knots much of the next 24 hours.

MARINE
Issued at 240 AM EDT Wed Apr 30 2025

Winds have subsided and will remain calm through Wednesday. The next concern will come late tonight into Thursday and the track of the low. Off shore flow will increase through the afternoon and evening with winds and waves potentially reaching SCY criteria for a brief period overnight Wed into early Thursday. As the low moves northwest from the south it will bring a stronger flow that will cause a wind shift to the southwest and will see winds increase after 10 AM Thursday morning. Winds and waves will increase and build into Thursday afternoon as the low passes. Given that the winds and waves are primarily due to the timing of the system will hold of on any products for the moment for increased confidence in its timing.

GRR WATCHES/WARNINGS/ADVISORIES
MI...Freeze Warning until 8 AM EDT this morning for MIZ037>040- 043>046-051-052.
Frost Advisory until 8 AM EDT this morning for MIZ050-056>059- 064>067-071>074.
MARINE...None.