Hawaii-Aleutian Daylight Time (HDT)
UTC offset: -09:00
Standard offset: -10:00 (HAST)
IANA identifier: America/Adak
Abbreviation: HDT
Population affected: approximately 5,000 (Aleutian Islands only)
DST period: Second Sunday in March to first Sunday in November
Hawaii-Aleutian Daylight Time is one of the most misunderstood US time zones because its name suggests Hawaii is involved. It isn't. Hawaii does not observe daylight saving time and stays on HAST (UTC-10:00) year-round. HDT applies only to the western Aleutian Islands of Alaska, specifically those west of 169° 30' W longitude.
This means approximately 5,000 people on a handful of remote Alaskan islands shift their clocks forward in March. The rest of the "Hawaii-Aleutian" zone (Hawaii's 1.4 million people) ignores DST entirely.
Why Hawaii Doesn't Observe DST
Hawaii is tropical (19-22°N latitude). Day length barely varies between seasons (about 11 to 13.5 hours). There's no practical benefit to shifting the clock. The state exempted itself from the Uniform Time Act of 1966, joining Arizona as the only US states that don't spring forward.
The Aleutian Islands
A volcanic archipelago stretching 1,900 km westward from the Alaska Peninsula toward Russia. The islands are fog-shrouded, windswept, and sparsely inhabited. Most of the population lives in Unalaska/Dutch Harbor.
Unalaska/Dutch Harbor (~4,700): America's busiest fishing port by volume. Pollock, crab, and cod processing dominate the economy. The TV show "Deadliest Catch" made Dutch Harbor famous. The weather is terrible: constant wind, sideways rain, temperatures hovering around freezing much of the year. The WWII Battle of Dutch Harbor (June 1942) was the first Japanese attack on American soil since Pearl Harbor.
Adak (~300): a former naval station, now a tiny civilian community. During the Cold War, Adak hosted up to 6,000 military personnel monitoring Soviet submarine activity. The base closed in 1997. The town has been slowly depopulating since.
WWII in the Aleutians
The Japanese occupied Attu and Kiska islands in June 1942, the only US territory occupied by a foreign power during WWII. The Battle of Attu (May 1943) was one of the war's bloodiest engagements relative to the forces involved. The Aleutian Campaign is sometimes called "The Forgotten Battle."
Practical Impact
HDT affects:
- Fishing fleet scheduling (departures, cannery shifts)
- Coast Guard operations
- FAA/aviation (Adak has an airstrip)
- Military timing (though the base is closed, some defense infrastructure remains)
The tiny population means HDT is largely irrelevant to broader US scheduling. It exists because federal law requires Alaska to observe DST, and the Aleutians happen to fall in the Hawaii-Aleutian time zone rather than the Alaska time zone.
Scheduling
At UTC-09:00 (HDT):
- Hawaii (HAST): 1 hour behind (Hawaii doesn't change)
- Alaska (AKDT): 1 hour behind
- US Pacific (PDT): 2 hours behind
- US Eastern (EDT): 5 hours behind
- Japan (JST): 18 hours ahead (effectively previous day)
During standard time (HAST, -10:00), the Aleutians and Hawaii are synchronized.
Neighboring Zones
| Zone | Offset (summer) | Difference from HDT |
|---|---|---|
| Hawaii (HAST) | UTC-10:00 | 1 hour behind |
| Alaska (AKDT) | UTC-08:00 | 1 hour ahead |
| US Pacific (PDT) | UTC-07:00 | 2 hours ahead |
| Samoa | UTC+13:00 | Date line split |
| Japan | UTC+09:00 | 18 hours ahead |
Technical Identifiers
- America/Adak (IANA canonical)
- HDT (Hawaii-Aleutian Daylight Time)
- HAST (winter: Hawaii-Aleutian Standard Time, UTC-10:00)
- Windows: "Aleutian Standard Time"
- DST rule: US schedule (2nd Sunday March, 1st Sunday November)
- Note: Hawaii uses "Hawaiian Standard Time" (no DST)
Quick Reference
| Attribute | Value |
|---|---|
| UTC offset (summer) | -09:00 |
| UTC offset (winter) | -10:00 |
| DST observed | Yes (Aleutian Islands only) |
| Hawaii DST | No |
| IANA zone | America/Adak |
| Population affected | ~5,000 |
| Key settlement | Unalaska/Dutch Harbor |
| Top industry | Commercial fishing |
| WWII history | Japanese occupation of Attu/Kiska |
| Same winter offset as | Hawaii |