Atlas No Ka Oi ( It's the best )

My Summary of Weather in Hawaii

I receive more email requests for weather information about Hawaii than any
other topic!

Here are my answers.

Temperatures in Hawaii are very stable because it is surrounded by a huge, deep, warm ocean. All the air over the islands must first pass over thousands of miles of that ocean before it reaches the islands. If the air comes from a cooler place, it warms up. If it comes from a warmer place, it cools off.

The ocean water temperature only varies from about 76 to 81 degrees F.

Here are typical sea water temperatures for Honolulu:

Honolulu, Oahu Island
Jan 76 Feb 76 Mar 76 April 76 May 78 June 79
July 80 Aug 80 Sept 81 Oct 81 Nov 79 Dec 77

Air Temperature
The air temperature follows a seasonal pattern. At sea level, the all day average air temperature varies from about 78 degrees in August to 72 degrees
in February.

Temperature varies depending on location. There are two main factors:
Altitude and exposure of the area to prevailing winds. The prevailing winds are
from the northeast. The northeast side of each island is called the windward side. The windward side of each island tends to be cooler and wetter. The high temperatures here
rarely reach 90° F.

The leeward side is warmer and drier, temperatures exceed 90° F several
days a year.

The temperatures at altitudes 1000 feet, very rarely drop to 50° F. Above 8000 feet, there is occasional freezing and even snow.

Precipitation
Snow is rare, but does occur at very high elevations, above 8000 feet.

Rain: Offshore, the rainfall is about 25 inches a year. As the warm, moist air passes over the islands, it must rise and cool as it passes over the hills and mountains. As it cools, water condenses. Therefore, the amount of rain
depends strongly on location.

The winds usually come from the Northeast. As those trade winds rise, they drop water on the land beneath them. Therefore, the windward side of the islands have much more rain than the leeward sides. In general, the closer you are to the mountains on the windward side,
( usually the northeast ), the wetter it is.

The air, having lost much of its water on the windward side, and warming again as it travels down the leeward side of the mountains, clears up. It's clouds dissipate and the rainfall diminishes.

The driest places are close to the ocean on the leeward,( usually southwest ) side of any island.

The rainiest time of year, in most places, is winter. The seasonal difference is greatest at moderate elevations, and small at elevations above 2000 feet.

Rain may be very heavy at times. Floods are not uncommon near rivers on the windward side of islands. See also, "Precipitation in Hawaii"

Winds
The trade winds that flow over and around the islands most of the time, must pass over mountains and through valleys. These winds are usually over 12 mile per hour. As they encounter these obstacles, wind speeds are increased as they pass through valleys and their direction changes as eddies form.

Winds may be gusty, strong and unpredictable as a result. Winds above 60 mph are rare events, occurring only about every five years.

Hurricanes
Hurricanes rarely hit Hawaii. Damaging hurricanes that do significant damage
have been separated by about 10 years on the average. These hurricanes are usually generated between Hawaii and Baja California. The most recent severe storm, Hurricane Iniki, struck Kauai and parts of Oahu in 1991.
See also, "Hurricanes in Hawaii"

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