What are the geographic bounds of the Central Pacific?
For purposes of hurricanes, the central Pacific is defined as north of the Equator between 140W and the International Dateline.
Why is there a mismatch between Storm Data zone codes and the descriptive text in Storm Data entries?
Zone numbers used to reference Storm Data changed in August 2004. Zone reference coding and descriptions (the red box in the figure below) for entries in Storm Data prior to August 2004 may not match the explanatory text. Customers should refer to the text entry below the date/time information for the correct area affected. From August 2004 to present, the zone numbers and areal reference are correct as entered.
What is the weather like in the winter (December, January, February)?
Winter is our rainy season, but that doesn't mean it rains all the time everywhere. Rather it is a time that the weather can be more unsettled and changeable as storm systems and cold fronts extend far enough south in the Pacific to impact Hawaii. When one of these weather systems affects island weather, it usually means several days with lighter winds, increased humidity and cloudiness with showers and heavier thunderstorms possible. It is unusual for any rain to last more than a few hours, so even on the wetter days, the sun usually shines. Still, about 50% of the time, normal tradewind weather dominates, which means a nice breeze with lots of sun and a few mainly brief and light showers, especially along east sides of the islands and near the mountains. Daytime temperatures are usually in the upper 70s with lows in the mid to upper 60s at lower elevations. After a cold front, it is possible for temperatures to dip into the 50s at night and only reach the low 70s during the day. If you go to the higher elevations on Maui and the Big Island, be prepared for cold temperatures and even snow. Temperatures above 10,000 feet will only reach the 40s during the day and 20s at night. At elevations above 12,000 feet it is normal for there to be several inches to feet of snow on the ground most days during the winter as those storm systems produce heavy snowfall at the summits. Those same storm systems are also responsible for frequent large surf along north and west sides of most islands. Surf higher than 25 feet occur many times each winter.
What is the weather like during spring (March, April, May)?
March is still considered to be part of our winter rainy season, but by April, patterns begin to change from the unsettled winter weather to more typical tradewind weather. Still, on average during the spring, about 60-70% of the time we experience tradewind weather. This means a nice breeze with lots of sun and a few mainly brief and light showers, especially along east sides of the islands and near the mountains. Most years, especially in March through early April, some of the tradewinds may become quite strong and blow at speeds of 30 mph and higher for a few days at a time. Daytime temperatures by May are usually in the lower to mid 80s with overnight lows in the upper 60s to lower 70s. If you go to the higher elevations on Maui and the Big Island, be prepared for cold temperatures. Temperatures above 10,000 feet will only reach the 40s to near 50 during the day and drop into the 20s at night. At elevations above 12,000 feet it is still possible for snow to occur, even into early May. Large surf episodes can still occur, especially in March.
What is the weather like during the summer (June, July, August)?
Summer weather is highlighted by the persistent tradewinds which occur about 90% of the time. These winds blowing from the northeast provide a cooling breeze accompanied by the occasional shower. The showers that occur tend to be brief and light in nature and confined to the windward, or east, sides of the islands and near the mountains. Daytime temperatures reach well into the 80s and even the lower 90s in some locations, especially the drier leeward sides. Overnight low temperatures are in the 70s. At higher elevations, such as Haleakala on Maui and Mauna Kea and Mauna Loa on the Big Island, temperatures are much cooler. Daytime highs will be in the 50s and 60s, with overnight lows in the 30s and 40s. During the 10% or so of the time that the tradewinds weaken, it can become rather humid. Hurricane season also begins in June, although it is not until late July and into August that the chances of a tropical system somewhere within the Central Pacific begin to really increase. On average, about 4 to 5 tropical systems occur each year within 1500 miles or so of Hawaii. The vast majority of the time, the storms stay far enough away that no impact is noted in Hawaii. The last time a tropical storm or hurricane came close enough to Hawaii was Jimena in 2003. It did not have a significant impact on the state. Summer is also the peak of our South Shore Surf Season. Large winter storms thousands of miles away in the south Pacific send swells toward Hawaii every week or so. Due to the large distance the swells have to travel, about the largest surf we experience along the south side of islands is 10 to 15 feet.
What is the weather like during the fall (September, October, November)?
These months are a transition time between the steady tradewind weather of summer and more unsettled weather during the winter. This is still hurricane season for the Central Pacific and Hawaii. On average, about 4 to 5 tropical systems occur each year within 1500 miles or so of Hawaii. The vast majority of the time, the storms stay far enough away that no impact is noted in Hawaii. The last time a tropical storm or hurricane came close enough to Hawaii was Jimena in 2003. It did not have a significant impact on the state. Typically the threat for tropical systems begins to quickly diminish by early October, however during El Nino periods, the threat can continue well into November. 1982 was a prime example, with Hurricane Iwa impacting Hawaii around Thanksgiving time. Tradewind weather is still the norm, occurring about 70% of the time but this pattern begins to fail more often during October and November as early winter storms in the North Pacific start reaching farther south. When the tradewinds fail, usually for 2 to 3 days at a time, it can become very humid. The threat for heavy showers and thunderstorms are also quite high during these brief periods. In fact, more flash flooding occurs during October than any other month. Still, the majority of the time the weather is dominated by tradewinds, meaning generally sunny conditions with brief light showers typically occurring along windward (east) sides of the islands as well as near the mountains. Daytime temperatures at low elevations during September into early October are still in the upper 80s to low 90s at times, but by November, highs are typically more in the mid 80s. Overnight lows are typically in the 70s. At higher elevations on Maui (such as Haleakala) and the Big Island (Mauna Kea and Mauna Loa)it will be much colder. Daytime temperatures will be in the 50s with overnight lows in the 30s. Beginning in October, it is possible for some snow to fall above 12,000 feet on Mauna Kea and Mauna Loa. By November, larger surf episodes are starting to take place along north shores of the islands as storms in the north Pacific are getting strong and sending larger swells our way.
Does it snow in Hawaii?
The answer is yes, although only on top of the highest peaks on Maui and the Big Island. Every winter, storm systems bring frequent snow storms to elevations generally above 11,000 feet. This means that only Mauna Kea and Mauna Loa are impacted. Many times these snowstorms are accompanied by strong winds, resulting in significant drifting of snow and blizzard conditions. Snow can occur in any month, but is most likely between October and April. Although routine snow measurements are not taken, during the winter of 2004-5, it is estimated that 35 to 55 inches of snow fell, and 40 to 75 inches during the winter 2005-6. Haleakala on Maui reaches just above 10,000 feet and snow is more rare there, occurring once every 2 to 3 years. On January 23, 2006, 1 to 2 inches of snow fell in association with a thunderstorm near the summit of Haleakala.
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