| Current Conditions | ||
| Temp |  | 3.5 C |
| RH | | 41 % |
| Wind | | NNE 14 mph |
| Road | | Open (4x4) |
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Hawaiian Islands Synoptic Discussion and Guidance 745 FXHW60 PHFO 190150 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 350 PM HST Fri Sep 18 2020 .SYNOPSIS... A high pressure ridge north of the island chain will keep moderate to locally breezy trade winds in the forecast through Sunday. Fairly stable conditions will keep shower activity brief for much of this weekend in the isolated to scattered coverage range. Trade wind speeds will decrease to more moderate levels through the first half of next week. No significant changes to the rainfall pattern for the next seven days. && .DISCUSSION... The big picture weather pattern remains unchanged with dry air moving over the Hawaiian Islands in a stable atmosphere. The subtropical ridge lingers north of the state will continue to produce moderate to locally breezy trade winds through Sunday. Trade winds will decrease through much of next week into a more moderate range as the high pressure ridge north of the Hawaii region weakens. Shower activity will remain relatively low for the next few days. Expect brief periods of isolated to scattered showers to continue through Sunday due to a low subsidence inversion heights between 5000 and 7000 feet that will limit vertical cloud development. In the longer range forecast for next week, model cross sections continue to show an increase in the inversion heights by Sunday. Typically higher thermal inversion heights will raise cloud tops and increase the potential for periods of showers into the forecast. However, current observational trends seem to favor a drier forecast at least in the short term. Longer range trends are showing a slight increase in shower activity through the first half of next week. However, atmospheric forcing is weak during this time period keeping our confidence in the higher rainfall trends at a moderate level. Dry fuels and low relative humidities will continue across the leeward areas each afternoon through the weekend. However, wind speeds are forecast to approach yet remain just below critical fire weather thresholds through Sunday. && .AVIATION... Expanding coverage of cirrus is damping diurnal mixing just enough to further suppress the already-limited coverage of cumulus and isolated light showers for Oahu through Big Island. This trend will continue for the remainder of the afternoon with nothing more than very isolated light windward showers anticipated. An uptick in coverage can be expected during the overnight hours, but VFR is forecast to persist through the forecast period. Trades will remain moderate out of the east. No AIRMETS are in effect. && .MARINE... Strengthening high pressure to the northeast of the islands has tightened the pressure gradient across the island chain, supporting Small Craft Advisory (SCA) winds through the typically windy channels around Maui County and waters south of the Big Island. These winds are forecast to hold through Sunday afternoon. Surf will be on the rise along north and south facing shores this weekend. Smaller-period, north-northwest swells will arrive today from strong to near gale force winds behind a northern Pacific cold front. This should provide a small bump along north and west facing shores tonight through Saturday. Long-period, south- southwest swells generated from last week's Tasman Sea storms will drive surf heights above the summer average over the weekend, but should stay below the advisory level of 8 feet. East shore surf will increase a touch due to strengthened trade flow. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST Sunday for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Bohlin AVIATION...JVC MARINE...TS Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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