National Weather Service United States Department of Commerce

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Issued: Feb 15, 2019 11:37 AM HST

Synopsis
A weak low east of the islands will lift northward through Saturday, then shift westward to the north of the state through the remainder of the weekend. This will gradually reduce the shower coverage and diminish the winds from east to west across the state today through the weekend. Unsettled weather appears to make a return during the early to middle part of next week, as deep tropical moisture lifts northward over the island chain. This could bring heavy rainfall, thunderstorms and the potential for flash flooding particularly to the central and eastern islands. Improving conditions appear in line by late next week.

Discussion
Quick update to issue a Wind Advisory for the island of Lanai through midnight tonight. Previous discussion follows:

Currently at the surface, a broad area of low pressure is located around 215 miles east of Hilo this morning, while a strong 1036 mb high is centered around 1350 miles north-northeast of Honolulu. The resulting gradient is producing breezy to locally windy north-northeasterly winds across the island chain this morning. Visible satellite imagery shows mostly cloudy skies in most windward areas, with partly cloudy conditions in leeward locales. Radar imagery shows scattered to numerous showers moving into windward areas, with some showers spilling over into leeward communities. Main short term concerns revolve around rainfall and wind trends through the weekend as the broad area of low pressure tracks westward to the north of the state.

Rest of today through Sunday night, The latest model guidance is in fairly good agreement showing the broad area of low pressure lifting northward through Saturday, then tracking westward well to the north of the islands Saturday night through Sunday night. Breezy to locally windy north- northeasterly winds will continue across the state today, with winds then gradually diminishing from east to west across the island chain tonight through Saturday night as the gradient relaxes. By Sunday and Sunday night, rather light winds are expected statewide, with daytime sea breezes and overnight land breezes expected in most areas.

Showery conditions will continue statewide today, with the most unsettled weather expected across windward areas, although a fair amount of leeward spillover will continue given the strong north- northeasterly winds. The cold temperatures aloft associated with the upper level low will maintain the potential for an isolated thunderstorm or two, mainly over the eastern half of the state. Also, some additional snow will remain possible over the summits of Haleakala, Mauna Kea, and Mauna Loa, and as a result a Winter Weather Advisory remains in effect through 6 PM this evening.

As the onshore flow diminishes from east to west across the state tonight through Saturday night, shower coverage and intensity will also trend downward in similar fashion from east to west across the island chain. Showers will continue to favor windward and mauka areas, with a few showers reaching leeward communities from time to time. By Sunday and Sunday night, winds will be light enough to allow for daytime convective shower development over mainly interior and mauka areas, with shower chances best along windward coastal areas at night.

Monday through next Friday, Model solutions are in fairly good agreement through the long term periods as well, with both the GFS and ECMWF indicating that more unsettled weather is in store for the island chain next week. Both models show the broad low or trough shifting westward and further away from the state early next week, while a strong 1045 mb high builds well to the north-northeast of the island chain. Meanwhile, an upper level trough west of the state will begin to induce low level troughing over the eastern end of the island chain early next week, with the models then indicating the potential for a low to develop along the trough and lift northward over the eastern or central islands around mid week. Both models show a tap into deep tropical moisture originating from the intertropical convergence zone, with precipitable water values climbing well above normal into the 1.5 to 2.2 inch range Monday night through at least Wednesday. This will bring the potential for widespread heavy rainfall and possibly thunderstorms to portions of the state, with the central and eastern islands appearing to be the favored targets at this time. By late next week as the low pulls further north and away from the state, drier air will work back into the region, reducing the shower coverage and intensity across the island chain.

Aviation
A surface low, to the east of the Big Islands, will start to move northwest later today/tonight. Currently, the low is helping to tighten the pressure gradient over the islands, producing fresh to strong north to northeast winds over most of the state. AIRMET TANGO for low level turbulence remains posted over the entire island chain. Winds will start to ease, from east to west, as the low moves into a position just north of the islands. High-res guidance shows light to moderate west to north winds from Maui County eastward by Saturday morning and moderate to fresh north winds from Oahu and west. It is likely AIRMET TANGO for low level turbulence will be scaled back to the western islands Saturday.

An upper level low over the state will help enhance clouds and showers, especially for mountain and windward areas. Isolated thunderstorms are possible today, mainly along the windward mountain and coasts, and northeast waters from Molokai through Big Island. Isolated light rime icing from flight levels 100 to FL250 is also possible in an areas of layered clouds just northeast of the Big Island and Maui. AIRMET SIERRA for mountain obscuration is posted across windward areas on all islands. Tempo MVFR to isol IFR CIG/VIS should be expected. This will likely continue for most of the weekend. Leeward areas should continue to see mainly VFR with passing showers with MVFR CIG/VIS today.

Marine
Strong high pressure far north of the state is currently being disrupted by a low located northeast of the Big Island. Winds will continue to be strong and gusty and out of the northeast for areas west of the Big Island through this afternoon and evening. Near the Big Island, winds will be a little more unpredictable due to the frequent showers and the low passing close to the area. But overall, winds will be mainly out of the north or northwest near the Big Island through this evening. The possibility for heavier showers and thunderstorms will remain near the Big Island and Maui County waters through this afternoon. As the low tracks north and west over the next few days, winds will begin to decrease in speed, and the direction will begin to shift to the north and then west over the weekend. Beyond the weekend, there is still quite a bit of uncertainty in the weather pattern due to an upper level low lingering near the state. But overall, winds will likely remain below Small Craft Advisory levels early next week.

The current northeast swell has decreased slightly compared to yesterday, but is still holding at heights well above normal. High Surf Advisories are posted for east facing shores through this afternoon, but will be extended at least through Saturday. A small to moderate northwest swell will begin to build on Saturday and is expected to peak at heights below advisory levels on Sunday.

A Small Craft Advisory (SCA) for all Hawaiian waters is posted through this afternoon, and will likely need to be extended for select zones as we get into the weekend.

Watches/Warnings/Advisories
High Surf Advisory until 6 PM HST this evening for Kauai Windward, Oahu Koolau, Olomana, Molokai Windward, Maui Windward West, Windward Haleakala, Big Island North and East.

Winter Weather Advisory until 6 PM HST this evening for Haleakala Summit, Big Island Summits.

Wind Advisory until midnight HST tonight for Lanai.

Small Craft Advisory until 6 PM HST this evening for all Hawaiian waters,


DISCUSSION...Jelsema

AVIATION...Eaton

MARINE...Kino