Winds over Hawaiian waters, especially in the channels between islands, are the most important weather element due to their high frequency of critical speeds and their effect on small craft and marine operations. Other than strong trade winds, strong winds aren't common over Hawaiian waters, but they do occur. Here's a look at Hawaii's trade winds, Kona winds, thunderstorm down-drafts, waterspouts, and winds associated with tropical storms or hurricanes.
Trade Winds
Accounting for 70% of all winds in Hawaii, trade winds are the most common winds over Hawaiian waters. These persistent winds, which blow from a NE to ENE direction, became known as trade winds centuries ago when trade ships carrying cargo depended on the broad belt of easterly winds encircling the globe in the subtropics for fast passage. Winds blow from each of the other quadrants (SE, SW, and NW) 10% of the time.During the summer, trades prevail more than 90% of the time, sometimes persisting throughout an entire month. However, in the winter, January through March, trade winds may occur only 40% to 60% of the time. Though pleasantly brisk and refreshingly cool on land, strong, gusty trade winds can cause problems for mariners. Blowing from the NE through East direction, these strong trades funnel through the major channels between the islands at speeds 5-20 knots faster than the speeds over the open ocean.
North Pacific high-pressure systems are responsible for the majority of gusty trade winds over Hawaiian waters, which commonly persist for several days before tapering off. Mariners and beachgoers must exercise good judgment before entering waters exposed to strong trade winds, especially in the major channels.
The following is a mean monthly frequency of the trade winds over Hawaiian waters/and strong trade wind percentages:
| Month | Percentage | Strong Trade Wind Days % |
| January | 42 | 9 |
| February | 55 | 7 |
| March | 61 | 10 |
| April | 74 | 10 |
| May | 86 | 7 |
| June | 91 | 7 |
| July | 95 | 10 |
| August | 94 | 7 |
| September | 83 | 4 |
| October | 71 | 4 |
| November | 64 | 8 |
| December | 57 | 9 |
Kona
Kona, a resort town on the leeward side of Hawaii's Big Island, is a Hawaiian term for the stormy, rain-bearing winds that blow over the islands from the SW or SSW, in the opposite direction of trade winds. The western or leeward sides of the islands, then, become windward in this case, as the predominant wind pattern is reversed.Kona winds occur when a low-pressure center is within 500 miles Northwest of the Islands and has an unusually low central pressure, below 1,000 millibars for the subtropics.
Although strong Kona winds usually don't last for more than a day, during this time they can cause considerable damage to boats caught in the open ocean or anchored in SW exposed anchorages. On land, the effects of strong Kona winds can be very dramatic. It's common for trees to be uprooted, branches downed, and roofs blown off houses. When reinforced by mountainous topography, downslope winds can gust over 100 mph, causing destruction in low-lying areas. On Oahu, the Schofield area below Kole Kole Pass in the Waianae Range and the Kaneohe-Kahaluu area below the Ko'olau Mountains has experienced extensive wind damage due to strong Kona winds.
Thunderstorm Winds
A thunderstorm is always accompanied by lightning and thunder, and may be accompanied by heavy rains, strong downdraft winds, hail and waterspouts. Occurring when a growing cumulus cloud turns into a cumulonimbus cloud, thunderstorms are exceptionally dense, and significantly vertical in development.Thunderstorms are uncommon in Hawaii, and are usually associated with cold fronts, Kona lows, or upper troughs between October and April. During the summer, tropical cyclones may also have thunderstorms embedded in their westward-moving cloud bands. The frequency of "thunderstorm days" in Hawaiian waters is very low on a monthly average, with one to three days a month during the winter, and zero to one day a month during the rest of the year.
However, thunderstorms are hazardous to marine interests because of the strong downdrafts, which may gust up to 60 knots (69 mph). The outflow from these downdrafts covers a few miles but lasts only a short time, about a half hour.
Waterspouts
Waterspouts and tornados are the same: small-diameter localized storms formed by winds rotating at very high speeds, usually in a counter-clockwise direction. The funnel is called a waterspout if it's over water and a tornado if over land. When a waterspout moves from water to land, it becomes a tornado. These severe storms of short duration develop from the base of heavy cumulonimbus, or thunderstorms (more commonly from cumulus clouds in Hawaii), and extend downward toward the sea.Hawaiian waterspouts are usually mild, and do not pack the devastating winds of midwestern tornadoes. However, the few severe waterspout or tornado incidents studied in Hawaii have indicated destructive wind speeds over 100 mph. The path of destruction is usually narrow, 50 to 300 feet wide, and less than a mile long, however, its speed of travel is faster than a boat.
Waterspouts occur mainly in the winter months, with the probability of one or two in November, December, January, or April. About 30-40 waterspouts are sighted annually in Hawaiian waters, although this is probably a small fraction of the true number of occurrences. Every waterspout has to be treated as though it will be a severe one, even though most waterspouts in Hawaii spin away harmlessly over the open water without causing damage.
Hurricanes and Tropical Storms
A hurricane is a severe large tropical cyclone originating over tropical oceans. Tropical cyclones to the left of the International Date Line (towards Asia), are called typhoons while tropical cyclones to the right of the International Date Line (towards Hawaii and Mexico) are called hurricanes.Tropical cyclones are classified according to their wind speed intensity.
There is a direct relationship between the central pressure of a hurricane and its maximum wind speed. The lower the pressure, the stronger the winds. The most intense tropical cyclones are the super-typhoons in the Western Pacific.
Hurricanes don't strike Hawaii often, with most of the threatening tropical cyclones weakening before reaching Hawaii, or passing harmlessly westward and south of the Islands. However, strong winds are always a potential threat from these rare storms, which can occur from June to November. Additional information on hurricanes can be found by visiting the PDC Hurricane page.