Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/21/17


Area Forecast Discussion...CORRECTED
National Weather Service Honolulu HI
335 PM HST Mon Mar 20 2017 .SYNOPSIS... A stable and rather dry trade wind flow will prevail into at least Friday, with limited rainfall confined to windward slopes. An increase in trades and windward rainfall is possible later next weekend. && .DISCUSSION... A 1022 mb surface high is passing about 600 miles north of the state this afternoon, while a deep ridge aloft sits over the islands. A shallow cloud band, the tail-end remnant of a front, is draped over the eastern end of the island chain and extends off to the northeast. This diffuse feature has dropped only a few hundredths of an inch of rain along windward slopes of Maui and the Big Island this afternoon, and Hilo sounding continued to show a low and strong inversion near 5000 ft. A dry slot to the north of this band is over Kauai and Oahu and is drifting southward, and recent aircraft and sounding data near these islands shows the inversion between 3000 to 4000 ft and precipitable water near an inch. Only minor fluctuations in the trade wind flow are expected through Friday. Moderate trade to locally fresh east-northeast trade winds will persist through tomorrow as the surface high moves steadily eastward. Trades will shift out of the east and may drop slightly over the northern end of the state by Wednesday as the high moves out and its associated ridge stalls about 300 miles north of Kauai. Stable and somewhat dry conditions will dominate most areas through at least Friday, with the inversion remaining rather low and strong in the 3000 to 5000 ft range. The cloud band currently affecting the eastern end of the state will produce modest rainfall over windward slopes of the Big Island tonight and possibly early Tuesday morning. Otherwise, expect limited rainfall over windward terrain during the next couple of days. The ECMWF and GFS models are hinting that moisture from the same cloud band may be briefly drawn back up over the Big Island on Thursday. Heading into the weekend, some changes are possible. Building high pressure to the northeast of the state will likely produce an increase in easterly trade winds. The ECMWF and GFS are both showing an upper level trough forming to the northeast of the state and possibly nearing the Big Island by Sunday. This feature could destabilize the trade wind flow and lead to an increase in showers. && .AVIATION... A high pressure ridge north of Hawaii will continue to produce moderate trade winds over the next few days. Expect prevailing VFR conditions with isolated showers possible over marine areas and along southern through western island slopes. Ceilings will tend to develop with isolated MVFR mainly over northern through eastern slopes of all islands, including scattered showers within the diurnal early morning and early evening time periods. There are no AIRMETs currently in effect. && .MARINE... A moderate northerly swell associated with a gale that passed around 800 nm north of the state over the past few days will continue to ease today. Surf will reflect this trend and steadily drop along exposed coasts. A moderate west-northwest swell associated with a storm-to-hurricane force low that developed near Japan a few days ago will continue to impact the islands today, but never really reached advisory- level surf (8 ft) along west facing shores of the Big Island. As a result, the high surf advisory has been canceled. A reinforcing west-northwest swell (310 deg) is expected to fill in through the mid-week period, but surf and seas should remain below advisory levels from this source. The latest ensemble and deterministic guidance remain in good agreement through the week and depict a large storm-force low developing near Japan Tuesday, then lifting northeast to the Aleutian Islands near the Date Line Friday through Saturday. If this feature evolves as predicted, a large westerly (290 deg) swell will result and likely impact the islands over the upcoming weekend with at least advisory level, potentially warning level, surf along exposed north and west facing shores. Small Craft Advisory (SCA)-level trade winds are forecast to continue across the typical windier waters through the first half of the week as high pressure builds north of the waters. The SCA is now in effect through early Wednesday morning. Trade winds may slightly weaken later in the week as a front passes far north of the state. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 AM HST Wednesday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ Public...Wroe Aviation...Bedal Marine...TS