Moderate easterly trade winds will continue into early next week. An upper level trough approaching the islands and will deepen into an upper low just north of Kauai today. This upper disturbance will pass slowly through the region and then linger northeast of the state into the weekend. Expect periods of enhanced clouds and showers across the region through the week. Shower activity will favor windward mountain areas in the overnight to early morning hours, with brief periods of showers drifting into leeward areas. Locations sheltered from the moderate easterly trade winds could also see increased clouds and a few showers during the afternoons.
The water vapor satellite imagery channel shows the upper level trough moving into the western islands this morning continues to deepen into an upper level low forecast to track slowly eastward through the island chain. This upper low will lift subsidence temperature inversion heights and enhance clouds and showers across the state. Windward mountains will see the highest shower activity during the overnight to early morning hours, while terrain sheltered leeward western mountains will see sea breeze trade wind convergence zones triggering enhanced showers during the afternoon hours each day.
The upper low and trailing upper trough will slow down and remain just northeast of the Hawaiian Islands into the weekend. The upper level lift just upstream of the islands will keep inversion and cloud heights elevated, allowing periods of showers to continue through the week. Only subtle day to day changes in island weather patterns are expected. This wet trade wind pattern may linger into the first half of next week as a shallow cold front and upper level trough approach the islands from the northwest. The wet season continues into the first week of May.
Moderate to locally breezy trade winds will continue during the next couple of days. Scattered to numerous shower activity can be expected over the next 24 hours or so across windward and mountain areas as an upper level trough moves across the region. AIRMET Sierra is currently in effect for windward areas across the state due to degraded cigs under showers, however this is expected to improve during the day today.
Moderate to fresh east-northeast trades will continue today before strengthening late tonight into tomorrow as a weak trough shifts to the west and a ridge builds north of the state. This will likely correspond to Small Craft Advisory winds across the typically windier waters surrounding Maui County and the Big Island beginning Wednesday.
A small bump in surf is expected today with the arrival of a small northwest swell. An upward trend is expected during the second half of the week as another northwest swell arrives. Looking further ahead, a storm- force low east of Japan will send a moderate, longer-period northwest swell toward the islands for Friday and Saturday, with surf heights potentially approaching advisory levels along exposed north and west facing shores.
Surf along south-facing shores will remain small through much of the week, with mainly background south to southwest swell expected. Another south-southwest pulse may arrive by this weekend from recent activity within our swell window east of New Zealand, providing a small increase in surf.
Surf along east-facing shores will remain relatively small and choppy through midweek, with a slight rise possible later in the week as trades strengthen.
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