Marine Weather and Tide Forecast for Grand Rapids, MI

DISCUSSION
Issued at 234 PM EDT Thu Oct 8 2026

- Brief chance of rain Friday night; then warm and sunny Saturday

Really no changes with the forecast through Saturday night for the area. various sources of model data all show a small and brief chance of rain coming through Friday evening into early Friday night. This remains associated with a sfc warm front and low level jet core of almost 30 knots passing through. Rainfall with this will be quite limited as moisture below 6k ft is quite limited, as is the window of opportunity with the forcing.

It will be noticeable on Saturday that we will be in the warm sector with steady warm winds blowing, and sfc temperatures well into the 70s. 850 mb temperatures around 16C will support those warm October temperatures.

- Rain chances with Isaias diminishing for Sunday

The most uncertain time frame in the forecast for the last few days has been centered around the Sunday time frame, due to the uncertainty with "Isaias" and the upper low that will be merging with it as it becomes extra-tropical in nature after making landfall along the Gulf coast.

The latest trend for it is to turn eastward a little quicker, and bringing just a chance of rain to the SE portion of the forecast area. We have been saying for days that the merging with a non- tropical upper low, and the movement of upper lows is quite uncertain. The 00z runs of the global models all trended east with it, after having trended NNW the previous couple of days before that. The latest trend is likely due to the atmosphere to its west being blocked up with a stronger ridge over the Mississippi River Valley, and the strong upper trough over the Western U
S

- Strong cold front Monday night/Tuesday with colder air to follow

The other trend we have noticed is that the rainfall amounts with the stronger cold front coming through Monday night and Tuesday have diminished a bit. The timing of the cold front has remained similar as previous runs, but qpf is on the lighter side overall. This looks to be a result from a lack of good Gulf moisture with Isaias taking much of it, and another good moisture feed not able to become established with the ridge immediately out ahead of it.

Much of the precipitation also looks to be right along, and behind the front as short waves in the upper flow ride along the front. We will see much cooler air advect in on the low level flow from the NE around an area of Canadian high pressure.

Beyond Tuesday/Wednesday has become more complicated as the large upper trough could possibly close off a low over the SW U.S., and potentially send more energy to the NE.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
Issued at 111 PM EDT Thu Oct 8 2026

VFR expected through the TAF period with diurnal Cu in the 4-6kft range this afternoon giving way to mid and high clouds tonight.
Northwest winds gusting to around 20 knots this afternoon favored to become light and variable tonight before increasing from the southwest Friday.

MARINE
Issued at 234 PM EDT Thu Oct 8 2026

We will hold on to the current Small Craft Advisory until the 5 pm expiration, as waves will still be up right around 4 feet until then for a few of the marine zones.

We will see a little bit longer of a break in the advisory conditions compared to the last break of only a few hours. The break should run from this evening into Friday evening, before winds and waves come up behind a warm front moving through. This period of wind will likely last through much of Saturday night before coming down on Sunday.

GRR WATCHES/WARNINGS/ADVISORIES
MI...None.
MARINE...Small Craft Advisory until 5 PM EDT this afternoon for LMZ844>849.