textproduct: Honolulu

SYNOPSIS

Residual moisture from Tropical Storm Lowell stretching into to Big Island and portions of Maui County may bring a renewed threat of heavy showers through this evening, while sea breezes trigger spotty afternoon showers across the rest of the state. Trade winds will slowly build over the state late tonight into Thursday, though moisture remains elevated across much of the state. Drier trade wind weather is expected to develop Thursday night into early next week.

DISCUSSION

Afternoon satellite water vapor imagery shows drier air in the low and mid levels spreading south into Maui County, with remnant moisture from Tropical Storm Lowell lingering across the Big Island. Scattered showers have developed from Molokai southward. Despite Precipitable Water around 2" further south, peak rainfall rates over the Big Island have only been around 0.50"/hr so far. Hi-res ensembles show little change in rainfall rates through the rest of the afternoon, increasing mainly on the windward sides of the islands tonight into Thursday morning as the band of tropical moisture shifts westward across the state and easterly flow strengthens slightly, and a few showers may spill over onto the leeward side. Instability remains marginal tomorrow, but enough to warrant a slight chance of thunderstorms with locally heavier rainfall over the interior of the Big Island this afternoon and again Thursday afternoon.

Friday through early next week, a large upper level low well northeast of the state and weak troughing aloft will allow for light to moderate trade winds to prevail with a more typical trade showers concentrated along windward locations in the night to early morning hours. Humidity will also decrease during this period as low-level drying occurs.

AVIATION

Tropical Storm Lowell remains north of the main Hawaiian Islands, and will continue to weaken and move further away from the islands. Surface observations along with satellite derived winds indicate trade winds are starting to affect the eastern islands along with the afternoon sea breeze. The trade winds are expected to spread through the remaining islands, and persist into tomorrow.

Moisture being pulled north from Tropical Storm Lowell, and this combined with sea breeze winds have enhanced clouds and shower activity over the Big Island, Maui, Molokai and Lanai. These islands are experienced periods of MVFR conditions, and even lower conditions on the Big Island, as such, AIRMET Sierra for mountain obscuration remains in effect and will be expanded to cover Molokai and Lanai. These additional clouds and showers will create more mountain obscuration, potentially lasting into early Thursday morning. Given the lower PWAT values for the western islands, will likely end the AIRMET for Kauai.

With light southerly winds expected, not anticipating any AIRMETs for turbulence today.

MARINE

A surface trough over the state will gradually move westward tonight. As the trough moves west, moderate to locally fresh trade winds will gradually return from east to west across the island chain through through Thursday and then persist into the weekend. The surface trough will bring some scattered showers across the area through Thursday.

The current moderate mid-period south swell continues to decline this afternoon and surf has dropped below advisory thresholds for south facing shores. This swell will continue to steadily decline over the next few days with below average surf expected by the weekend.

Surf along east facing shores will gradually decrease tonight and will remain near seasonal averages through around Saturday due to east and northeast swells generate by former tropical cyclones. Surf along north facing shores continues to receive a small bump due to Lowell. This short-period northwest swell will quickly fade, allowing surf to become tiny along north facing shores on Thursday as Lowell weakens and tracks away from the islands.

FIRE WEATHER

Fire weather risk will remain low the next several days due light winds and lingering moisture. Expect a slight chance of thunderstorms over the Big Island this afternoon and again Thursday afternoon. Temperature inversion heights are expected to remain elevated or weak.

HFO WATCHES/WARNINGS/ADVISORIES

None.