Current Conditions
Temp7.4 C
RH60 %
WindN 10 mph
RoadOpen (4x4 only)
Mauna Kea Observatories Forecast
5 PM HST Friday 28 August (0300 UTC Saturday 29 August) 2015
Warning(s)
Small chances for episodes of high relative humidity
Cloud Cover and Fog/Precipitation Forecast
There is a small risk for fog as humidity lingers in the 50-70% range through the night. There is a possibility for linger patches of mid-level clouds for this evening. High, broken cirrus might be visible along the NW horizon. No precipitation expected tonight.
Summary of Key Meteorological Variables
Summit temperatures will be near 3.5 C tonight and tomorrow morning. Winds will be light and from the NNW, with seeing around 0.55-0.6 arcseconds. Precipitable water is expected to exceed 4 mm through the night.
Discussion
The air masses over the island has stabilized a bit and a weak inversion is present at about 7 thousand feet. Nevertheless the lingering mid-level moisture will allow humidity to linger in the 50-70% range likely through Saturday evening. Consequently, there is a small risk for periods of fog, particularly during the evening hours over the next 2 nights. Tropical moisture and instability are expected to build in from the ESE beginning early Sunday morning, and may help breakdown the inversion and signicantly increase the risk for extensive fog, rain and convection for Sunday through Tuesday night. Some afternoon clouds are likely over the next few days, then will likely turn extensive for Sunday and early part of next week.

There is a possibility for lingering patches of mid-level clouds (from afternoon clouds) for this evening and high clouds may be visible along the northwestern skies, dissipating through the night, leaving predominately clear skies for most of Saturday. However, there is a possibility that bands of clouds may begin to fill in from the ESE early Sunday morning, with thicker more widespread clouds following suit for later that night and early part of next week.

Precipitable water is expected to exceed 4 mm throughout the forecast period.

Light winds will prevail at and above the summit and seeing is expected to be in the average to less than average range through Saturday night. There is a possibility that building turbulence in the atmosphere will start to degrade seeing early Sunday morning and contribute to bad seeing for the following 3 nights. Observing conditions are likely to be unoperable from Sunday and onward.

Not much is chanced since the morning forecast... The low-level ridge to the North of the State will maintain a certain degree of subsidence/stability in the area for at least 24 more hours, but a weak mid-level flow will allow moisture to persist in the area and keep humidity and PW near 50-70% and 4-8 mm, respectively, over the next 2 nights. This is likely to result in episodes of fog and high relative humidity at times, through Saturday night. Beyond that, conditions near the Big Island depends upon Hurricane Ignacio. The last model runs has been consistently showing Ignacio to pass just to the north of the Big Island (as a hurricane and dangerously close) around Monday; rainbands out ahead of the storm are expected to reach the area as early as sunrise Sunday and sticking around into the middle part of next week. While it should come to no surprise that there is a lot of uncertainty with respect to the track and intensity of this storm and especially its impact to lower elevation areas, the copious amount of widespread deep tropical moisture surrounding the storm is a bit more certain/consistent and very likely to negatively impact summit conditions for Sunday and Monday night. Thus, there is a very good chance that another round of extensive fog, clouds and rain will plague the summit (as well as deep/widespread convection in the area) for those nights. Please, keep monitoring the Central Pacific Hurricane Center outlook/discussion over the next few days.
WRF Astronomical Observing Quality Guidance
Cloud Cover and Precipitable Water Analyses
MK CN² Profiles
5 Day Forecast Summary (Graphical Trend)
HST Cloud Fog/Precip Temp Wind Seeing PW
Cover (%) Height (km) Probability (%) (Celcius) (Dir/MPH) (Arcseconds) (mm)
Fri Aug 28 - 8 PM10-307-830 / 04.5N/5-150.51-0.816-12
Sat Aug 29 - 2 AM20-407-810 / 03.5NNW/5-150.4-0.76-10
2 PM30-503-560 / 1010NNW/10-20NaN4-8
8 PM0-20Clear40 / 04N/10-200.4-0.86-12
Sun Aug 30 - 2 AM0-20Clear20 / 03N/5-150.4-0.86-12
2 PM30-503-570 / 306NNE/5-15NaN10-20
8 PM50-703-680 / 603NE/15-251-1.410-20
Mon Aug 31 - 2 AM80-1004-790 / 601.5NNE/15-251-1.410-20
2 PM80-1004-790 / 805N/25-45NaN10-20
Tue Sep 01 - 2 AM80-1004-790 / 802.5NW/25-451-1.410-20
2 PM80-1004-790 / 804W/20-40NaN10-20
Wed Sep 02 - 2 AM80-1004-790 / 802SW/15-251-1.410-20
2 PM80-1004-790 / 803S/10-20NaN10-20
Rise and Set times for the Sun and Moon
Night (HST) Sun Set Twilight End Twilight Beg Sun Rise Moon Rise Moon Set Illumination (%) RA DEC
Sat Aug 29 - Sun Aug 30 18:49 19:55 4:51 5:57 18:42 N/A 99 23 06.5 -4 44
Sun Aug 30 - Mon Aug 31 18:48 19:54 4:51 5:57 19:31 N/A 96 0 05.1 0 02
Mon Aug 31 - Tue Sep 01 18:47 19:53 4:52 5:57 20:19 N/A 90 1 03.1 4 43
Tue Sep 01 - Wed Sep 02 18:46 19:52 4:52 5:58 21:07 N/A 81 2 00.7 9 00
Wed Sep 02 - Thu Sep 03 18:45 19:51 4:52 5:58 21:56 N/A 71 2 57.9 12 35
Forecast Issued by: Tiziana Cherubini
Next update at 10 AM HST (2000 UTC) Monday 31 August 2015.
Additional Information
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