| Current Conditions | ||
| Temp |  | 7.4 C |
| RH | | 70 % |
| Wind | | NNE 13 mph |
| Road | | Closed |
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Hawaiian Islands Synoptic Discussion and Guidance 089 FXHW60 PHFO 161959 AFDHFO Area Forecast Discussion National Weather Service Honolulu HI 959 AM HST Mon Sep 16 2019 .SYNOPSIS... Moist and unstable conditions associated with an upper disturbance and surface trough of low pressure in the vicinity of the islands will keep the potential for heavy showers in the forecast through this evening. A return of drier air and more stable conditions is anticipated from east to west Tuesday through the second half of the week. Increasing moisture and rain chances will become a possibility once again over the upcoming weekend. && .DISCUSSION... At the surface, a 1026 mb high is centered about 1400 miles north of Hawaii. A passing trough to the north between the islands and the high is allowing for the otherwise moderate to fresh trade winds to veer east southeasterly across the smaller islands this morning. Water vapor imagery shows an mid to upper low centered about 400 miles north northwest of Hawaii that will gradually be lifting northwest over the next day or so. Southwest winds along the eastern flank of the low is currently drawing scattered to broken midlevel clouds across the central and eastern parts of the state as shown on visible satellite. A few low clouds are anchoring along the windward slopes as well. MIMIC Total Precipitable Water (PW) shows a swath of PW near 2 inches across the state and 12Z soundings show a weak inversion. Dew points are mainly in the upper 60s to low 70s at the sea level observation stations. The upper low will keep conditions unstable today, especially across the western half of the state. Localized sea breezes may set up leeward and along the northwest coasts allowing for clouds and showers to develop this afternoon into the early evening similar to yesterday. Can't rule out a few of these showers becoming heavy at times. Conditions will gradually begin to improve over the eastern end of the state by late tonight into Tuesday, as drier air and more stable conditions move in from the east. Guidance remains in decent agreement Tuesday night through the second half of the week and reflects a return of drier and more stable conditions statewide. The low-level flow (up to 10,000 ft) is forecast to shift back to a more typical easterly direction and strengthen. Model PWs should drop back to and around normal through this period. Clouds and showers will focus over windward and mountain areas, especially through the overnight and early morning periods as pockets of higher moisture move through from east to west. Despite some differences between the various model solutions, a return of light winds and increasing moisture (two inch PWs) will be possible next weekend as a trough associated with a tropical disturbance to the south moves through. Added instability associated with an upper low setting up over the state combined with this moisture will support increasing rainfall chances. && .AVIATION... Elevated moisture will keep low clouds and showers around for today and into the overnight hours. Brief periods of MVFR conditions are possible, particularly for windward areas. Winds are in the light to moderate category out of the east-southeast. A drying trend with increasing trades is on tap as we head into Tuesday thanks to the upper low north of Kauai moving away from the state. AIRMET Zulu remains in effect for light icing 160-FL280. && .MARINE... High pressure far north of the state is expected to strengthen slightly and slowly move east through the week. This will lead to moderate to locally strong easterly trades through most of this week. Winds may veer to the southeast across the far western Hawaiian waters near the middle of the week as a low pressure system tracks south to north, west of the state. The Small Craft Advisory (SCA) remains in effect for waters around Maui and the Big Island through this afternoon. We will continue to monitor the winds today to see if the SCA needs to be extended. Nonetheless, borderline SCA level winds are expected for Monday night into Tuesday. A series of small swells from the southwest, south, and southeast is expected this week. The largest of these swells looks to be towards the end of the week as a combination of a long-period south-southwest swell and potential short-period southwest swell moves in across the area. Surf heights are expected to be below advisory levels with these swells. Small surf is expected along north, east and west facing shores through the new week. Expect a small east swell from Tropical Cyclone Kiko as early as Wednesday along exposed east facing shores and likely continuing through the weekend. Exposed west shores may see some of the aforementioned southwest swell on Friday. A small northwest swell will be possible late in the weekend into early next week. && .HFO WATCHES/WARNINGS/ADVISORIES... Small Craft Advisory until 6 PM HST this evening for Maalaea Bay- Pailolo Channel-Alenuihaha Channel-Big Island Windward Waters- Big Island Leeward Waters-Big Island Southeast Waters. && $$ DISCUSSION...Foster AVIATION...Dye MARINE...Powell Bulletins, Forecasts and Observations are courtesy of Honolulu National Weather Service Forecast Office |
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