This alert expired on 4 September 2026 at 10:45 UTC. It is kept here as a record.
It is the 4th strongest of the 7 detections recorded within 20 km of this point since 10 June 2026. The last comparable one was on 27 July 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
Nearby, since 10 June 2026
- June 10, 2026 · score 28 · 8.0 km
How we know
Confirmed by 2 independent sources, including NOAA.
Our own score for this event is 16 out of 100, at 67 % 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) | 16 / 100 |
| Our confidence | 67% |
| Coordinates | 43.4600, -87.1350 |
| Nearest City | Sheboygan (56 km) |
| Impact Tier | minor |
| 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; Sheboygan to Port Washington WI; Port Washington to North Point Light WI; Lake Michigan from Sheboygan to Port Washington WI 5NM offshore to Mid Lake; Lake Michigan from Port Washington to North Point Light WI 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 |
| MergedCount | 2 |
| MergedIds | ["noaa_urn:oid:2.49.0.1.840.0.0190815737d01c3b279e58207085537e00d0c4dd.001.1","noaa_urn:oid:2.49.0.1.840.0.e6f8f081d27159c8b6fdd76b1e3b6e92371549f5.001.1"] |
| Iem TypeSummary | M |
| Iem Magnitude | 44 |
| Iem Unit | MPH |
| Iem City | 1 ESE Sheboygan |
| Iem County | LMZ643 |
| Iem State | WI |
| Iem Wfo | MKX |
| Iem Remark | SGNW3 Sheboygan lighthouse reported 38 kt wind gust. |
| MergedSources | [{"id":"iem_M_43.750_-87.690_1788508800000","source":"iem","severity":"low","severityValue":25,"timestamp":1788508800000,"latitude":43.75,"longitude":-87.69}] |
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 16/100 (United States), based on data from noaa. Source: Calamity.live, a platform aggregating real-time data from 185 scientific monitoring sources.