textproduct: Honolulu

SYNOPSIS

A broad, building high north of the islands will produce a tight pressure gradient leading to breezy to windy trades over the next couple days. Enhanced shower activity and cloud coverage will remain mainly over windward and mauka areas. As the high meanders northeastward away from the islands later this week, trades will weaken to a more moderate regime for the remainder of the week.

DISCUSSION

The latest model guidance continues to support a broad, building high situated well north of the Hawaiian Islands. Currently at 1034 mb, this area of high pressure produces a tight pressure gradient -- the key factor in the recent breezy to windy trades across the state and progged to prevail throughout the remainder of the week. Trades are anticipated to be strongest on Wednesday, as the aforementioned high is progged to build to around 1035 mb. This has increased confidence for more widespread windy trades and may exceed wind advisory thresholds beyond the typical wind- prone locations. However, have opted to hold off on issuing a wind advisory at this time for models to better assess timing and location in a future shift. Thereafter, deterministic guidance suggests the high will begin to weaken and and propagate northeastward away from the islands during the latter half of the week. Trades will respond accordingly, weakening as well, though is expected to remain moderate to locally breezy.

Throughout the week, the enhanced trades will bring periods of shower activity, particularly across windward and mauka areas across all islands. Latest model guidance has depicted a weak low and associated frontal boundary developing east of the island chain early Wednesday that is set to meander further eastward and dissipate. Prior to dissipating, however, moisture associated with the frontal boundary gets embedded in the enhanced trade wind flow, suggesting an uptick in shower activity along windward and mauka areas, namely across Maui and the Big Island. Latest GFS total precipitable water (PWAT) Normalized Anomaly depicts PWATs to be 1 to 2 standard deviations above normal during this time. Conversely, the ECMWF isn't quite as high, but still remains wetter than normal, showing 0 to 1 standard deviations above normal. Either way, expect windward trade showers to be prominent throughout the middle of the week, then gradually lessen through the weekend.

A slightly drier air mass will keep dew points in the low- to mid-60s through the next several days, presenting a more Fall-like ambiance across the islands. Relative humidity values may take a brief hit today and tomorrow, with values falling below 50 percent today, predominately across leeward Big Island, recovering back above 50 percent as the week progresses as additional moisture moves into the state.

In the longer range, by early next week, some model guidance indicates an influx of an abundance of moisture will be pulled northward and engulf the Hawaiian Islands as a surface trough produces southerly flow. Model PWAT Normalized Anomalies during this time are suggesting PWAT values upwards of 3 standard deviations above normal; the first indication that heavy rainfall may be in the future. However, confidence remains low at this time, given the long lead time before the event. That said, future shifts will need to monitor model trends to determine how accurate this initial assessment proves to be.

AVIATION

Breezy to locally windy trades persist through the day, leading to embedded clouds and enhanced shower activity over windward and mauka areas. MVFR conditions are possible in heavier showers. Otherwise, VFR conditions prevail.

AIRMET Tango remains in effect for mechanical turbulence to the lee of the mountains of all islands due to the breezy trade winds. This is expected to continue through the next couple days.

MARINE

A strong ridge of surface high pressure, centered roughly 1000 nm north of the islands will maintain fresh to strong trades across all marine zones today. In addition, combined seas are expected to surpass 10 feet for windward marine zones and through island channels. Trades are then forecast to further increase tonight through Thursday and become strong to near gale force. A Gale Warning may be need during the peak of the event for the typically windy waters surrounding Maui and the Big Island. The high will gradually drift eastward and weaken Friday, leading to moderate to fresh trades through this weekend.

A short to moderate period, north- northeast (020-030 deg) swell, generated from strong trades near and upstream of the islands, will produce large and rough surf above High Surf Advisory (HSA) levels along north and east shores today. The northerly component to the swell, at least to start the day (before the swell direction becomes more northeasterly), will allow for surges at north facing harbors, mainly Hilo and Kahului. A Marine Weather Statement remains in effect to highlight this. In addition, a combination of higher than predicted water levels, large breaking waves, and strong onshore winds could lead to significant wave runup, beach erosion, and localized coastal flooding near this mornings high tides for north and east facing shores, then mainly for east facing shores thereafter during daily peak high tide cycle. The HSA will likely be dropped for north facing shores tonight and extended for east facing shores through at least Wednesday night, as large waves and choppy conditions persist from strong to near gale force trades around and upstream of the islands. The advisory may need to be upgraded to a warning during the peak of the event on Wednesday, as surf heights approach warning criteria of 15 ft. Northeast swell energy lowers on Thursday as local trade winds begin to decline, with east shore surf steadily dropping Friday through the weekend.

A pulse of long period south swell energy has arrived and can be noted on the near shore buoys this morning at around 3 feet 14 seconds. This swell is progged to peak slightly higher late today into Wednesday, then begin to fade by Thursday. This late season energy should help bump surf up to near or slightly above the November average. South shore surf returns to near flat Friday into this weekend.

FIRE WEATHER

Breezy to locally strong trades will continue across the state through the week. Relative humidity may briefly fall into the mid- to upper-40s today for isolated leeward areas, however, low-level moisture embedded within the trades should prevent this from being widespread. Additional areas of moisture moving into the state should help to keep relative humidity from reaching critical thresholds for the remainder of the week. Inversion heights will remain around 6,000 to 7,000 feet today.

HFO WATCHES/WARNINGS/ADVISORIES

High Surf Advisory until 6 PM HST this evening for Niihau-Oahu North Shore-Olomana-Maui Windward West-Kauai North-Kauai East- East Honolulu-Koolau Windward-Molokai Windward-Molokai Southeast- Molokai North-Maui Central Valley North-Windward Haleakala- Kipahulu-Big Island East-Big Island North.

Small Craft Advisory until 6 AM HST Thursday for all Hawaiian waters-