Overview and answer to the main question
Hurricane Irma occurred mainly during late August and early September 2in the North Atlantic. It formed from a tropical wave on August 30, intensified into a major hurricane over the next few days, and made landfalls in the Caribbean and the United States in early September. The core period of activity spans August 30 to September 12, 2017, with the most destructive impacts concentrated September 6–10. Irma was a long-lived Cape Verde–type hurricane and one of the strongest on record to affect the northern Leeward Islands and Florida.
How tropical cyclones are tracked and dated
Tropical systems are dated by the time they first reach a specific intensity or designated status. Agencies use formation time (tropical depression), tropical storm designation, and major hurricane milestones. Forecast and advisory products are timestamped to communicate changes in threat. For long-term reference, “when did Hurricane Irma happen” is answered with a sequence of key dates rather than a single day.
Key dates and milestones in the lifecycle of Irma
The timeline below summarizes verified milestones based on post-season analyses from official sources. Dates and times are given in Coordinated Universal Time (UTC).
| Date/Time (UTC) | Event | Why it matters |
|---|---|---|
| August 30, 06:00 UTC | Tropical Depression Six formed east of Cabo Verde | Start of the official trackable system |
| August 31, 18:00 UTC | Strengthened to Tropical Storm Irma | Named storm began to organize further |
| September 2, 18:00 UTC | Became a Category 3 major hurricane | Crossed into major hurricane status |
| September 4, 12:00–18:00 UTC | First landfalls in the Leeward Islands (Barbuda, Saint Martin, Virgin Islands) | First significant land impacts; sustained Category 4 winds |
| September 6, 11:15 UTC | Landfall in Cudjoe Key, Florida (U.S.) | First U.S. landfall as major hurricane |
| September 7, 06:30 UTC | Second U.S. landfall in Marco Island, Florida | Continued widespread impacts across Florida |
| September 8–10 | Tracking across the southeastern U.S. as a tropical cyclone | Continued effects including wind, storm surge, and flooding |
| September 12, 00:00 UTC | Dissipated over Georgia | End of the system’s identifiable circulation |
Timeline context for regions affected
- Leeward Islands: First U.S. territory and island nations encountered the strongest winds on September 6–7.
- Florida: Major hurricane conditions arrived September 6 into September 7, with prolonged impacts due to size and slow movement.
- Southeastern U.S.: The region experienced wind, rain, and tornado threats through September 9–10 as Irma weakened but continued moving northward.
- Track notes: Irma’s unusual westward early track, then northward turn influenced where the worst winds and surge occurred.
Measuring and comparing Irma’s intensity
Intensity is commonly summarized using categories and metrics that remain useful for comparison over time.
| Metric | Value for Irma | Context |
|---|---|---|
| Maximum 1-minute sustained winds | 185 mph (295 km/h) | Near peak intensity on September 6 |
| Minimum central pressure | 914 mb | Reflected extreme intensity in the open Atlantic |
| ACE (Accumulated Cyclone Energy) | ~64–68 (estimated) | Reflects long-duration strong winds |
| Saffir–Simpson Category | Category 4 at U.S. landfall | Based on sustained wind at the time of landfall |
Practical context for using the timeline today
Understanding when Hurricane Irma happened helps with preparedness planning, historical comparisons, and interpreting recovery timelines. The dates show how a long-lived system can affect multiple regions sequentially. For ongoing reference, this timeline supports risk communication, education, and planning well after the event.
Common questions and clarifications
Because Irma affected areas over several days, people often ask for clarification.
- What single date is most associated with Irma’s U.S. impacts? September 6–7, 2017, when major hurricane conditions occurred in the Florida Keys and parts of South Florida.
- Did Irma only impact coastal areas? No, inland areas experienced damaging winds, flooding rainfall, and tornadoes for days after landfall.
- When should I review preparedness steps? Use this timeline annually in late summer/early September and update kits and plans based on local guidance.
Reliable sources and further context
Key sources include the National Hurricane Center’s official Tropical Cyclone Report for Irma, National Weather Service service assessments, and NOAA best practices. These provide the dates above and support accurate, consistent communication about past events and future preparedness.