We’ve just entered our first rainy period since last Spring. The weather is cool at night by Hawaii standards, high 60’s, and the rains are consistent. These conditions are forecast to continue through the rest of this week, if not longer.
What does this mean for your Hawaii vacation? Between November and April expect at least one month of rain. That averages to 15 percent of the time in those six months.
The rain is a love and hate thing for me, inasmuch as I know that we need it. This is what keeps Hawaii beautiful, fills the reservoir, and keeps Muley’s grass growing. At Beat of Hawaii’s headquarters on Kauai, we typically get over 100 inches of rain annually.
On the other hand, during these weather conditions, it just isn’t the Hawaii that we or our visitors think of. If it rains long and hard enough, the otherwise clear and beautiful ocean fills up with dirt and runoff, and becomes unswimmable.
Today’s rain started me thinking about the weather here in Hawaii and how we see it from a local perspective. Our seasonal weather variations are quite unusual, as compared with the U.S. mainland:
- Cool, “Ho’oilo” Season
September begins with cooler nights which then leads to cooler and shorter days. It’s coolest from about December to March, before gradually returning to warmer conditions. During this season you can expect an average high of 77 during the day and an average low of 62 at night.
- Warm, “Kau” Season
From May to Labor Day, expect longer and hotter days and balmier nights. During this season our average high is 82 degrees and low of 70 when the sun goes down.
- Wet weather comes in two segments
The first in either November or December, and the second sometime between February and April. The most common rainy months are November and March. When these winter rains arrive, they are typically not geographically specific, and can equally impact all parts of all the islands.
- Dry Season, May to October
Dry weather prevails the rest of the year, although dry doesn’t exactly mean dry. Dry weather here includes “mauka” or mountain showers.
These rains, driven by the trade winds, typically cross the higher elevations from the northeast to the southwest of the islands, leaving the south and west sides warmer and dryer. Most of the rain is deposited in the mountains and valleys, turning dry at the coast, which typifies our micro-climatic conditions.
It is often possible to have sun and warmth only a block away from cool and rain. During these “dry” conditions, you can typically escape from any rain by heading to nearby drier areas.
- Trade winds prevail more than 80 percent of the time
Typical Hawaii trades are based on subtropical high pressure ridges that bring cool winds from the north. They also provide lovely clear conditions, and a cooling effect during otherwise warm periods. Trade winds are also associated with dry weather and mauka rain conditions.
- Still or south Kona wind
When the winds stop or blow from the south, which is less than 20 percent of the time, the weather here isn’t optimal. In the winter it will tend to be cold and wet and in the summer, humid. South winds are common during periods of heavy winter rains. In recent years, Kona winds also allow the VOG to move up from the Big Island and cover the other main islands.