Start date and what it means for Hurricane Katrina
Hurricane Katrina began as a tropical wave that moved off the west coast of Africa on August 23, 2005. That same day, the wave organized enough to be designated a tropical depression. It strengthened into Tropical Storm Katrina later on August 23, then into a hurricane on August 27, and rapidly intensified into a major hurricane just before making its first U.S. landfall. The "start date" is most precisely identified as August 23, 2005, when the National Hurricane Center initiated advisories on Tropical Depression Twelve. The following timeline shows how Katrina evolved from that initial tropical wave into one of the costliest and most destructive hurricanes on record.
| Attribute | Verified Detail | Source Type |
|---|---|---|
| Tropical wave origin date | August 23, 2005 | National Hurricane Center (NHC) archive |
| Tropical depression formation | August 23, 2005 (12:00 UTC) | NHC public advisory |
| Named storm formation (Katrina) | August 24, 2005 (03:30 UTC) | NHC best track |
| Hurricane status | August 27, 2005 (06:00 UTC) | NHC best track |
| Major hurricane (Category 3+) status | August 27, 2005 (18:00 UTC) | NHC best track |
| First U.S. landfall (Southeast Louisiana) | August 29, 2005 (06:10 UTC) | NHC best track |
Why people ask about the start date
People ask about Hurricane Katrina's start date because the term is often used to refer either to when the storm first organized (August 23) or when it became a major hurricane and made landfall (late August 29). For forecasting and emergency management, the relevant start is when the system was first identified as a tropical depression. The date August 23, 2005, is consistently cited in official NHC reports as the beginning of the event that led to catastrophic impacts in Louisiana, Mississippi, and Alabama.
From tropical wave to named storm
On August 23, 2005, a tropical wave exited the African coast and quickly showed signs of low-level circulation. By the afternoon (UTC), the National Hurricane Center classified it as Tropical Depression Twelve while it was centered well east of the Lesser Antilles. Six to eight hours later, with improved organization and sustained winds reaching 40 mph, it became Tropical Storm Katrina. This early development phase was monitored closely because conditions ahead—warm sea surface temperatures and light upper-level winds—were favorable for further intensification.
Key early milestones at a glance
- August 23, 2005, ~12:00 UTC: Tropical Depression Twelve forms; National Hurricane Center begins advisories
- August 23, 2005, ~18:00–21:00 UTC: Strengthens into Tropical Storm Katrina
- August 24–25: Katrina moves west-northwest across the Atlantic, slowly intensifying amid favorable environmental conditions
- August 26: Rapid deepening begins; Katrina becomes a Category 1 hurricane
- August 27: Becomes a Category 3 major hurricane; Gulf Coast states begin significant emergency preparations
Official records and best-track data
The National Hurricane Center's authoritative "Best Track" dataset is the standard reference for dates and intensities. The entries below are drawn from the NHC’s post-storm analysis and include the times and classifications used by forecasters and researchers. Times are given in Coordinated Universal Time (UTC).
| Date and Time (UTC) | Event | Significance |
|---|---|---|
| August 23, 12:00 UTC | Tropical Depression Twelve designated | Start of the official record for Katrina |
| August 23, ~18:00–21:00 UTC | Upgraded to Tropical Storm Katrina | Named storm begins; easier to communicate risk |
| August 25 | Passes southeast of the Bahamas | Continues to organize while moving toward the Gulf |
| August 27, 06:00 UTC | Becomes a Category 1 hurricane | First hurricane status |
| August 27, 18:00 UTC | Becomes a Category 3 major hurricane | Major hurricane threshold reached; heightened preparedness needs |
| August 29, 06:10 UTC | First U.S. landfall (Southeast Louisiana) | Major hurricane at landfall; catastrophic impacts follow |
Key distinctions in how Katrina is referenced
Because Katrina evolved over several days, different contexts use different reference points:
- Meteorological start: August 23, 2005, when the tropical depression formed
- Major hurricane start: August 27, 2005, when Katrina became a Category 3
- Landfall-centric references: Late August 28–29, 2005, when the most devastating impacts occurred in New Orleans and along the Gulf Coast
Emergency planners and media reports often emphasize the later dates because those are tied directly to warnings, evacuations, and impacts. However, for climatological records and forecast verification, the official start remains the date the system was first declared a tropical depression.
Common clarifications
Some confusion arises because Katrina's most catastrophic effects happened days after the initial formation. The storm underwent rapid intensification in the Gulf of Mexico on August 28–29, becoming a severe Category 5 over the Gulf before weakening slightly at landfall. The start date does not imply when the worst impacts occurred, only when the system was first monitored as a tropical cyclone. Forecast models on August 23–24 already showed the potential for major Gulf Coast impacts, which is why long-lead warnings and preparations began early.
Summary of the start
Hurricane Katrina started on August 23, 2005, when the National Hurricane Center designated the system as Tropical Depression Twelve. It became Tropical Storm Katrina later that day, a hurricane on August 27, and a major hurricane on August 27 before making its first U.S. landfall as a catastrophic storm on August 29. The official record uses August 23 as the event's beginning, which is essential for consistent historical comparisons, forecasting practices, and public communication.