A weak but fast-moving cold front continues to make its way towards the state and expected to bring an increase in showers with the possibility of pop-up thunderstorms on Hawaii Island Tuesday evening (February 9th) through Wednesday (February 10th) to a lesser extent on Thursday (February 11th).
Published by: HIRSC - Weather Team
A fast-moving cold front will sweep down the island chain through Tuesday, bringing a relatively short period of widespread clouds and showers, and a chance for thunderstorms. Cool and breezy northerly winds will strengthen after the front passes, bringing low clouds and a few showers to northern exposures. Winds will become moderate trade winds Wednesday through Friday, bringing gradually increasing windward showers. Southeast winds may bring a further increase in moisture starting next weekend.
The front continues its advance down the island chain. Just before sunset, the front started to move over Oahu, bringing widespread clouds and showers to the island. By 8 pm, the back edge of the cloud band was along the north shore of Oahu and the leading edge was moving over the western shores of Molokai. Some thunderstorms have been observed along the line, however, the number of thunderstorms has diminished since sunset, and the intensity of showers has decreased. Ahead of the front, a couple of thunderstorms popped up near Maui and the Big Island, but both were short-lived. Have updated the forecast for the first half of the night to include mention of thunderstorm possibilities out ahead of the front. Have also modified the PoPs and associated fields behind the front over Kauai to better reflect the clearing trend. Have also lowered the PoPs and associated fields for parts of Oahu during the second half of the night. Cool, northerly winds have spread across Kauai behind the front, and those winds are expected to spread across Oahu overnight. Dewpoints on Kauai are in the upper 50s, and those will also spread across the state behind the front. The front was in the Kaiwi Channel at 8 pm, moving faster than originally expected. Anticipate it moving over Maui County in the next couple of hours, and reaching the Big Island late tonight, clearing the Big Island by Tuesday night. The associated moisture is expected to move to the east of the islands and could be carried in on the trades later this week. The front itself is still expected to bring some thunderstorms with it, as cold air aloft is reaching -18 C at 500 Mb. Some gusty winds are also possible with the frontal passage, but this frontal passage is not expected to be impactful as the last. The cold air aloft will lead to a lowering of the freezing level to below 10000', bringing the potential for wintry weather on the Haleakala Summit as well as the Big Island Summits. A Winter Weather Advisory has been issued, with the potential for fairly short-lived impacts to occur. Haleakala will likely experience the main winter weather impacts tonight, with the Big Island Summits being impacted late tonight/early Tuesday, possibly lingering into Tuesday night on the Big Island if moisture is slow to clear. Cool and breezy north to northeasterly winds will strengthen after the front passes, driving dew points into the lower 50's (F), and bringing a renewed chill to the islands. These winds may deliver a few low clouds and light showers to N facing slopes and coasts. Peak wind speeds during the day Tuesday may be strong enough to warrant a Wind Advisory, especially where terrain most accelerates the flow on Maui and the Big Island, and over Lanai. A gradually warming and moistening air mass is expected Wednesday through Saturday, as surface high pressure tracks steadily east along 30N, with the focus for clouds and showers shifting back to the typical windward areas. As the low aloft exits the area to the east, a dramatic warming is expected at 500 mb, supporting a very stable island atmosphere, with limited shower coverage and intensity. Moderate trade winds are expected to veer to the southeast through the weekend, with some of the pooled frontal moisture sliding back toward the islands, potentially as early as Friday. Guidance shows moisture increasing further early next week as another mid-level low induces a surface trough over the islands, potentially fueling more widespread showers.
A fast-moving cold front will continue its march southeastward across the state. As of 8 pm HST, the front was over the Kaiwi Channel and expected to reach Molokai and Lanai by midnight and the remainder of Maui county by morning. The front is expected to rapidly deteriorate as it moves across the Big Island Tuesday morning. Expect heavy showers, gusty winds, and possible thunder and lightning along and immediately ahead of the front. Partial clearing and strong northwest winds lie in the wake of the front. AIRMET Sierra for current or expected mountain obscuration is currently in effect for Oahu, Molokai, Maui, and Lanai. Sierra has been canceled for Kauai due to improved ceilings and will likely be canceled for Oahu by midnight. Winds will veer from west-northwest to north northeast Tuesday afternoon as the front fades and exits the area. Winds will be breezy to locally strong both tonight and Tuesday. A return to dry light to moderate trade wind flow is expected Tuesday night. AIRMET Tango has been posted for low-level mechanical turbulence to the lee of higher terrain. Tango currently includes Kauai and Oahu but will likely need to be expanded to included Maui County by morning. The front is being strengthened by a digging upper-level trough that trails the surface feature. This could result in moderate upper-level turbulence late tonight or Tuesday morning for Oahu, Maui County, or the Big Island.
A cold front moving through the central island waters this evening will continue to move southeastward into the Big Island by Tuesday morning, and east of the islands by Tuesday night. Periods of showers are forecast along the front with isolated thunderstorms. Gentle northwesterly winds ahead of the front will shift to breezy to locally strong north winds by early Tuesday morning, becoming northeasterly trade winds across the region by Tuesday afternoon. A Small Craft Advisory (SCA) remains in effect for all coastal waters due to increasing winds and elevated seas with a rising northwest swell. This SCA will decrease in coverage over the western waters on Wednesday as trade winds decrease and seas lower from west to east. The SCA will likely be canceled for all waters by Thursday morning. Another large northwest swell will arrive on Friday with an SCA likely going up again for Hawaiian waters exposed to northwest swell. The next northwest swell will continue to build through the overnight and early morning hours, peaking from Tuesday afternoon to Tuesday night. Surf heights are expected to rise into advisory levels along most north and west of the smaller islands from Tuesday afternoon through Wednesday morning. This swell will lower from Wednesday into Thursday as the forerunners of a new large northwest swell arrive by early Friday morning. A new long-period northwest swell will rise quickly on Friday. Surf heights will likely reach High Surf Warning levels late Friday through Sunday. The swell and surf heights will then slowly lower through the first half of next week. Surf along east and south facing shores will remain on the small side through the next seven day forecast period.
High Surf Advisory from noon Tuesday to 6 AM HST Wednesday for Niihau, Kauai Windward, Kauai Leeward, Waianae Coast, Oahu North Shore, Oahu Koolau, Olomana, Molokai, Maui Windward West, Windward Haleakala. Winter Weather Advisory until 6 PM HST Tuesday for Haleakala Summit, Big Island Summits. Small Craft Advisory until 6 PM HST Tuesday for all Hawaiian waters.