This alert expired on 4 September 2026 at 10:45 UTC. It is kept here as a record.
It is the 6th strongest of the 11 detections recorded within 20 km of this point since 3 April 2026. The last comparable one was on 22 August 2026.
What the source measured
NOAA reported: Special Marine Warning issued September 4 at 4:39AM EDT until September 4 at 6:45AM EDT by NWS Grand Rapids MI
An estimated 62,609 people live within 50 km of this point.
Nearby, since 3 April 2026
- May 16, 2026 · score 39 · 5.1 km
- May 13, 2026 · score 39 · 13.5 km
- June 9, 2026 · score 39 · 13.6 km
How we know
One source: NOAA. Not yet confirmed by a second, independent source.
Our own score for this event is 32 out of 100, at 82 % confidence.
The score is ours, computed from intensity, exposed population and local history — not the source’s.
Computed under scoring rules v4. Rows carrying other versions were judged by different rules and are not directly comparable.
Event Data
| Type | Severe Weather |
| Severity | Medium |
| Calamity Score (ours) | 32 / 100 |
| Our confidence | 82% |
| Coordinates | 43.3817, -86.6775 |
| Nearest City | Muskegon (38 km) |
| Population Exposed | 62.6K within 50 km |
| Impact Tier | significant |
| Timestamp | 2026-09-04T08:39:00.000Z |
| Source | https://api.weather.gov/alerts/urn%3Aoid%3A2.49.0.1.840.0.0190815737d01c3b279e58207085537e00d0c4dd.001.1 |
Score Breakdown
Technical Details
| Event | Special Marine Warning |
| Urgency | Immediate |
| Certainty | Likely |
| AreaDesc | Holland to Grand Haven MI; Grand Haven to Whitehall MI; Whitehall to Pentwater MI; Lake Michigan from Pentwater to Manistee MI 5NM offshore to Mid Lake; Lake Michigan from Whitehall to Pentwater MI 5NM offshore to Mid Lake; Lake Michigan from Grand Haven to Whitehall MI 5NM offshore to Mid Lake; Lake Michigan from Holland to Grand Haven MI 5NM offshore to Mid Lake; Lake Michigan from South Haven to Holland MI 5NM offshore to Mid lake |
| Headline | Special Marine Warning issued September 4 at 4:39AM EDT until September 4 at 6:45AM EDT by NWS Grand Rapids MI |
| Expires | 2026-09-04T06:45:00-04:00 |
| SenderName | NWS Grand Rapids MI |
| HasExactCoords | true |
Safety Information
Always follow official guidance from your local emergency management agency. This platform provides scientific monitoring data and is not a substitute for official warnings. If you are in immediate danger, contact your local emergency number.
Series begins 8 March 2026. Comparisons refer to that period only. Collection gap: 14-26 August 2026.
This data is aggregated algorithmically from scientific sources. Not a replacement for official emergency warnings.
Want to know when something happens in this area?
Calamity.live data shows a weather event with CalamityScore 32/100 (United States), based on data from noaa. Source: Calamity.live, a platform aggregating real-time data from 185 scientific monitoring sources.