textproduct: Grand Rapids

KEY MESSAGES

- Becoming Hot and Humid

- Rain Chances Increase Tonight into Sunday

- Additional Chances for Rain and Thunderstorms Next Week

DISCUSSION

Issued at 216 PM EDT Sat Aug 29 2026

- Becoming Hot and Humid

An upper-level high will develop over the southern CONUS and migrate toward the southeast CONUS by midweek. Southwesterly low- level flow from the southern plains will transport 850 mb temperatures around 20 C over Lower Michigan from late Sunday through Tuesday or Wednesday. At the surface, a warm front in the area on Sunday should progress north on Monday, with high temperatures inland favored to reach the upper 80s to lower 90s. Ensembles point to Wednesday potentially being the hottest day before a majority of the solutions shunt the heat south of the area on Thursday. With the dew points climbing toward 70 degrees, the heat index could climb to 95-100 degrees Mon-Wed.

- Rain Chances Increase Tonight into Sunday

North of a surface warm front tonight into Sunday, a layer of moisture and clouds amid weak instability is streaming in around 700 mb / 10,000 feet. With relatively drier air beneath, the current batch of rain inbound from Wisconsin will weaken to just light rain around Ludington and sprinkles elsewhere this evening. Additional moisture / higher theta-e at that layer advecting in late tonight into Sunday, along with MUCAPE gradually increasing above 500 J/kg, will support the development of numerous showers and embedded thunderstorms. DCAPE is relatively weak on Sunday, though with the drier low-level air in place with 35 knot winds a couple thousand feet above the surface, occasional 30-40 mph wind gusts could get mixed down on Sunday.

- Additional Chances for Rain and Thunderstorms Next Week

Precipitation chances are lower on Monday as most of the activity should lift north out of the area with the advancing warm front. The pattern will be rather unsettled through at least Tuesday and Wednesday as we will be on the northern edge of the heat dome, with quasi-zonal flow that will contain upper-level jet streaks and shortwaves. CAPE generally around 1000-2000 J/kg will be present, with the question being when might moisture layers or lift mechanisms help break the cap. The timing of such chances for storms is uncertain at this point, though given adequate deep- layer shear also present, a marginal risk of severe weather could eventually manifest.

AVIATION /18Z TAFS THROUGH 18Z SUNDAY/

Issued at 129 PM EDT Sat Aug 29 2026

Regional radar shows light rain moving east across Wisconsin. There's quite a bit of dry air in place over Michigan and much of the rain will evaporate prior to reaching the terminals. Nonetheless, a few showers are possible later this evening and overnight, mainly east of JXN/LAN. VFR conditons expected through the period.

MARINE

Issued at 216 PM EDT Sat Aug 29 2026

Southwest winds built up 2 to 4 ft waves earlier this morning around Grand Haven and Muskegon, but waves will overall settle into the 1 to 3 ft range this evening.

Small craft advisory and beach hazards statement is likely needed for north of South Haven early Sunday morning and through the day. It may also be needed for south of South Haven, at least due to wind speeds if not waves, but this is lower confidence. The base state of winds on Sunday, given the pressure pattern, is 15 to 25 knots from the south. Various model solutions offer some additional complexity to the wind forecast, as areas of elevated rain showers and thunderstorms early Sunday morning may perturb the pressure field, and enhance or decrease wind speeds within some zones of Lake Michigan.

Generally the 15-25 knot winds Sunday morning will be focused over the southern half of Lake Michigan, and the 06 and 12 Z runs of the HRRR suggested an area of gales accelerating out from higher pressure underneath a batch of rain showers or thunderstorms for part of the morning. There may also be a narrow break in the wind field bisecting the middle of the lake Sunday morning also, with less confidence in the wind speeds north of Whitehall. Then modeled winds from the southwest also get squirrelly over southern Lake Michigan Sunday afternoon, depending on how any additional batches of showers/storms evolve. The result is fair confidence in 3-6 foot waves and high swim risk between South Haven and Ludington on Sunday.

GRR WATCHES/WARNINGS/ADVISORIES

MI...Beach Hazards Statement from 2 AM EDT Sunday through Sunday evening for MIZ037-043-050-056-064. MARINE...Small Craft Advisory from 2 AM to 11 PM EDT Sunday for LMZ844>849.