An upper-level low northeast of the islands will remain nearly stationary through today, enhancing clouds and showers with moderate to locally breezy trade winds prevailing. This weekend, the upper low is forecast to move northeast away from the state, and wind speeds will decrease slightly. Mainly windward and mauka showers are expected, with limited spillover into leeward areas. Moderate trades will prevail into early next week, followed by lighter flow a land/sea breeze pattern thereafter.
Early morning satellite and radar imagery shows scattered to numerous showers moving into windward and mountain sections of the islands. While a few select windward locations across Maui and Big Island have received more than half an inch since yesterday evening, most locations have received much less with relatively light rainfall rates observed.
Moderate to breezy trade winds will continue for the next several days as a series of high pressure systems move from west to east across the North Pacific. An upper-level low that has lingered about 600 miles northeast of the state for the past several days will remain in place through today, keeping some cold air aloft over the region. This will result in some local instability producing deeper clouds and enhanced shower coverage across windward and mauka areas, with isolated showers reaching leeward areas. This instability will support occasional moderate to briefly heavy showers throughout this period.
Trade wind speeds should weaken slightly this weekend as the upper-level low exits the region to the northeast, though periods of showers will continue to favor windward and mauka areas. Moderate trades will continue into early next week, but confidence is increasing that a weaker ridge north of the state could reduce background wind speeds further by Tuesday. This scenario would support daytime sea breezes and nighttime land breezes beginning as early as Tuesday and lasting through much of next week.
A stationary upper-level low remains anchored northeast of the state and will enhance cloud and shower activity across windward mountain areas, resulting in occasional MVFR/IFR conditions. Otherwise, moderate to locally breezy trades are expected to prevail under VFR conditions through the forecast period.
AIRMET Tango remains in effect for tempo moderate turbulence across leeward sides of all islands below 8000 feet due to the breezy trade winds. Expect this AIRMET to continue throughout the day. AIRMET Sierra will also go into effect for mountain obscuration for Oahu through the Big Island.
Fresh to strong easterly trades will persist through tonight as strong high pressure remains north-northeast of the state. As a result, the Small Craft Advisory remains in effect for all Hawaiian waters today. Winds will gradually ease over the weekend as the ridge weakens in response to a front passing far north of the islands. This downward trend should allow winds to fall below advisory levels across most, if not all, waters by the end of the weekend, with similar conditions lingering into Monday. Trades are then forecast to ease further Tuesday through midweek, potentially allowing a land and sea breeze pattern to develop near the coasts.
Surf along exposed north and west-facing shores will build above early May averages this weekend due to a relatively active northern Pacific pattern for this time of year. Although offshore buoys have yet to detect this new swell energy, long-period northwest (320 deg) forerunners are expected to arrive later this morning, leading to a gradual increase by late this afternoon. Surf heights could approach advisory levels tonight into Saturday, particularly if the swell arrives larger than currently forecast. This swell will then gradually ease through the weekend. Another, slightly smaller northwest pulse is expected early next week, maintaining elevated surf along north and west-facing shores. Looking ahead, guidance indicates yet another long-period northwest (320 deg) swell may arrive late next week, generated by a developing storm near Japan that is forecast to lift northeast near the Kuril Islands over the weekend.
Surf along south-facing shores will trend up over the weekend as a long-period south-southwest pulse arrives. Expect a peak later in the weekend and into Monday before lowering.
Surf along east-facing shores will remain rough today in response to the strong trades locally and upstream. A downward trend is then anticipated as the trades ease over the weekend.
Small Craft Advisory until 6 PM HST this evening for Kauai Northwest Waters-Kauai Windward Waters-Kauai Leeward Waters- Kauai Channel-Oahu Windward Waters-Oahu Leeward Waters-Kaiwi Channel-Maui County Windward Waters-Maui County Leeward Waters- Big Island Windward Waters.
Small Craft Advisory until 6 AM HST Saturday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters.
