Weather Details & Aloha Paragraphs

The trade winds, at least for the moment, will be our main driver in the Hawaiian Island weather picture…aided in part by the passage of an upper level trough of low pressure. The combination may be able to trigger briefly heavy showers. There has been some evidence of this upper air feature, with its associated cold air aloft…as some towering cumulus clouds have been reported recently. The Kona slopes on the Big Island have seen locally heavy rains, falling at a rate of 2.50" per hour in places…which is pretty intense! An more robust upper low could influence our area more directly as we get into the Friday-Sunday time frame, forming as what we call a Kona low to the NW of Kauai.

Meanwhile, our latest weather map shows our trade wind producing high pressure cells far to the north and NE Wednesday evening. The high pressure cell to the north, up to the north of 40 degrees of latitude, will be moving swiftly eastward. As we move into Thursday, this high will be just offshore from the southern Washington coast. An active cold front, issuing from a low pressure system in the eastern Gulf of Alaska, will weaken our high pressure to the north. This in turn will begin to erode our trade wind air flow, making our local trade winds softer….and turning them clockwise to the southeast by Friday. SE winds put most of the islands in the wind shadow of the Big Island, with much lighter winds than we’ve seen over the last week expected. SE winds too can bring volcanic haze into the picture, especially over the Big Island and Maui.

These lighter winds will take us out of the trade wind weather pattern that is currently active, pushing us into what we call a convective weather pattern. This strongly suggests that our local cumulus clouds will have no reason to not climb higher into the sky than normal. We call these kinds of clouds towering cumulus. As you can well imagine, after looking at those types of turrets, heavy showers can easily fall from their bases. The one wild card remains just how the upper low will influence our local weather? The first level of uncertainty involves exactly where and how deep the upper low will be when it gets closest to the Hawaiian Islands this weekend. The second is just how much moisture will be drawn up over the islands by the SE winds.

If, and it’s still definitely an if, all the ingredients come together just right, we could see good soaking showers…mostly during the afternoon hours in the upcountry areas. Then again, if one part of the puzzle is missing, either the upper level low’s proximity, or the lack of moisture to feed the convective showers is missing….then all bets are off. It will likely take another day or even two before we know for sure which way the pendulum will swing. The NWS office in Honolulu hasn’t issued a hydrologic outlook, which typically signifies the good chance of a heavy rain event. The models continue to flip flop from one solution to the next. Just for reference, the latest GFS model run shows a deep kona low forming to the west-northwest of Kauai, with 35 mph SE winds drawing up lots of moisture…which would cause a heavy rain event with flooding! However, it seems premature to go with more than the chance of heavy rains occurring here in the islands this weekend at the moment.

It’s Wednesday evening here in Hawaii, as I begin updating this last paragraph of today’s narrative. As noted above, the trade winds will stick around through Thursday, then get knocked down by an upper level low pressure center moving near the islands starting Friday. It’s a straight forward fact that the trade winds will be going on vacation. Whether this Kona low will bring us rain, or even locally heavy showers, is another story. It appears that the low will get close enough that our atmosphere will become unstable. Instability can certainly prompt heavier showers, no doubt about that. The wild card then becomes just how much moisture is around to feed those showers! If the expected southeast winds can draw upon rich moisture from the deep tropics, then we should see some good soaking showers in the upcountry areas each afternoon from Friday through early next week. However, if that moisture doesn’t arrive, we could see nice weather, although rather hot and sultry…with little more than cloudy afternoons with localized showers falling. We may have to wait another day or so before we will know for sure what will manifest. ~~~ The islands may have good weather for the most part, even with that area of low pressure in our vicinity. The mornings especially will tend to be nice, with those pesky clouds building up over the mountains starting late in the mornings, through the rest of the daylight hours. ~~~ In the by the way department, I had to slam on my brakes this morning when driving down the back way towards Pukalani, as three little baby wild pigs ran across the road in front of me! Here on Maui, in Lahaina town, there is a famous event on Front street, where all the Halloween festivities occur. They often refer to this night out on the town as the Mardi Gras of the Pacific. Here’s a few pictures of one of those Lahaina Halloween nights in the past – 1 – 2 – 3 – 4. I will be back early Thursday morning with your next new weather narrative from paradise, and hopefully even some further clarification about the possible increase in showers through the rest of the week. I hope you have a great Wednesday night wherever you happen to be reading from! Aloha for now…Glenn.