Latest Forecast for Mauna Kea Observatories
10 AM HST (2000 UTC) Wednesday 08 August 2018

Warnings
Fog, high humidity and rain
Moderate/strong (diminishing) winds

Cloud Cover and Precipitation Forecast
Fog, high humidity and light rain will continue to plague the summit throughout the night. Banding thick clouds are expected to stream in from the SE and contribute to extensive cloud cover through the night.

Summary of Key Meteorological Variables
Summit temperatures will be near 6.5 C this afternoon, 2.5 C this evening and 3 C tomorrow morning. Winds will be from the ESE at 35-50 mph for today, diminishing to 15-30 mph by the end of the night. Seeing and precipitable water are expected to exceed 1 arcsecond and 4 mm, respectively through the night.

Graphical Summary

Discussion
The atmosphere below 18 thousand feet will remain fairly saturated through early tomorrow evening, then will begin to slowly dry out as the inversion restrengthens near 10 thousand feet by sunrise Friday. Nonetheless, extensive fog, high humidity and light rain will continue to plague the summit for tonight and probably most of tomorrow night. There is also an outside chance for the development of isolated convection in the area, particularly along the southern half of the Big Island through tomorrow afternoon. Drier more stable conditions are set to return to the summit, once the inversion reaches full strength near 6-8 thousand feet for Friday, Saturday and Sunday night. Extensive daytime clouds are expected through tomorrow, then will taper for Friday, become minimal and short-lived for the weekend, only to pick up again for the early part of next week.

Banding thick clouds are expected to stream in from the SE, contributing to extensive cloud cover, if not overcast skies for tonight and probably most of tomorrow night. These clouds will eventually shift off toward the west and SW on Friday, leaving predominately clear skies for that night and Saturday night. However, another band of high clouds may move in from the SE during the second half of Sunday night.

Precipitable water is expected to exceed 4 mm for the next 2 nights, slip toward 2.5-3 mm for Friday, Saturday and at least the early part of Sunday night (it may trend toward 4 mm through the latter night).

While the boundary layer turbulence is set to diminish over the next 24 hours, a steady supply of moisture will contribute to poor/bad seeing through tomorrow night. A drier air mass, combined with relatively light laminar easterly flow aloft should allow seeing to improve early Friday evening and eventually settle in near 0.5-0.6 arcseconds during the second half of that night and Saturday night. There is a possibility that an increase in free atmospheric turbulence may degrade seeing toward more average-like values through Sunday night.

TC Hector will continue to slide westward, passing about 300 km to the south of the Big Island later this afternoon. While this will help rapidly diminish summit-level winds over the course of the night, deep tropical moisture along its northern flank will keep the atmosphere below 18 thousand feet rather saturated during that time. A secondary influx of moisture drawn in from the SE along the passing storm's eastern flank is also expected to arrive during the second half of the night, then will shift westward through tomorrow night. Nonetheless, this abundant supply of tropical moisture will allow extensive fog, high humidity, overcast skies and light rain to the plague the summit for tonight and probably most of tomorrow night. There is also an outside chance for the development in convection in the area, but that should be limited to the SE and SW flanks of the Big Island and perhaps within the plume to the west. Dry/stable and clear/calm conditions/skies are set to return to the summit as Hector shifts far west of the state and the ridge to the NE regains control of the air mass, rebuilding the inversion near 6-8 thousand feet for Friday, Saturday and Sunday night. An upper-level low is expected to develop to the east of the Big Island and transverse westward late in the weekend. Initially the low will have little to no affect on summit conditions and may also allow relatively deep NE flow to prevail in the free atmosphere, which should help seeing to settle in near 0.5-0.6 arcseconds for much of the weekend. However, the low could begin to destabilize the air mass and bring high clouds in from the tropics as it progresses westward and over the state for the early part of next week.

Astronomical Observing Quality Guidance
05 pm HST Wednesday 08 August (03 UTC Thursday 09 August)CN2
08 pm HST Wednesday 08 August (06 UTC Thursday 09 August)CN2
11 pm HST Wednesday 08 August (09 UTC Thursday 09 August)CN2
02 am HST Thursday 09 August (12 UTC Thursday 09 August)CN2
05 am HST Thursday 09 August (15 UTC Thursday 09 August)CN2
08 am HST Thursday 09 August (18 UTC Thursday 09 August)CN2
Latest WRF CN2 Profiles Animation | Collage


5-day Forecast
Summary

Graphical Trend
02 pm HST
Wed 08 Aug
08 pm HST
Wed 08 Aug
02 am HST
Thu 09 Aug
02 pm HST
Thu 09 Aug
08 pm HST
Thu 09 Aug
02 am HST
Fri 10 Aug
02 pm HST
Fri 10 Aug
08 pm HST
Fri 10 Aug
02 am HST
Sat 11 Aug
02 pm HST
Sat 11 Aug
02 am HST
Sun 12 Aug
02 pm HST
Sun 12 Aug
02 am HST
Mon 13 Aug
00 UTC
Thu 09 Aug
06 UTC
Thu 09 Aug
12 UTC
Thu 09 Aug
00 UTC
Fri 10 Aug
06 UTC
Fri 10 Aug
12 UTC
Fri 10 Aug
00 UTC
Sat 11 Aug
06 UTC
Sat 11 Aug
12 UTC
Sat 11 Aug
00 UTC
Sun 12 Aug
12 UTC
Sun 12 Aug
00 UTC
Mon 13 Aug
12 UTC
Mon 13 Aug
Cloud Cover (%) 80 to 100 80 to 100 80 to 100 80 to 100 80 to 100 60 to 80 20 to 40 0 to 20 0 to 5 0 to 20 0 to 5 0 to 20 40 to 60
Cloud Height (km) above sea level 4-10 4-10 4-10 4-10 6-10 9-10 N/A N/A N/A N/A N/A N/A 9-10
Chance for Fog/Precip (%) 100/90 100/90 100/90 95/90 80/40 60/20 20/0 0/0 0/0 0/0 0/0 0/0 0/0
PW (mm, summit upward) 6 to 10 8 to 12 8 to 12 8 to 12 6 to 10 4 to 8 3 to 6 2.5 to 3.5 2.5 to 3.5 2.5 to 3.5 2.5 to 3.5 2.5 to 3.5 3 to 5
Mean Seeing (arcsecs) N/A 1.4 ± 0.4 1.2 ± 0.4 N/A 1.1 ± 0.3 0.9 ± 0.2 N/A 0.6 ± 0.1 0.55 ± 0.1 N/A 0.55 ± 0.1 N/A 0.65 ± 0.15
Summit Temp (°C) 6.5 2.5 3 7 3 3 8 3 2 6.5 0.5 6 0
Wind Dir/Speed (mph)
    Summit (615 hPa)
    19,000 ft (500 hPa)
    24,500 ft (400 hPa)
    31,000 ft (300 hPa)
    35,000 ft (250 hPa)
    40,000 ft (200 hPa)
    46,000 ft (150 hPa)
    54,000 ft (100 hPa)

E/35 to 50

ESE/25 to 40

ESE/15 to 30

ESE/10 to 20

E/10 to 20

ESE/10 to 20

ENE/10 to 20

ENE/10 to 20

ENE/10 to 20

ENE/10 to 20

ENE/10 to 20

SE/5 to 15

S/5 to 15


 Rise and Set times for the Sun and Moon
Night (HST)
Sun Set
Twilight End
Twilight Beg
Sun Rise
Moon Rise
Moon Set
Illum (%)
RA
Dec
Wed.Aug.08/Thu.Aug.09
19:04
20:13
4:42
5:51
4:00
N/A
6
7 20.9
19 58
Thu.Aug.09/Fri.Aug.10
19:03
20:12
4:43
5:51
5:06
17:53
1
8 23.9
18 31
Fri.Aug.10/Sat.Aug.11
19:03
20:11
4:43
5:52
6:12
18:50
0
9 25.6
15 44
Sat.Aug.11/Sun.Aug.12
19:02
20:10
4:44
5:52
N/A
19:43
2
10 24.9
11 55
Sun.Aug.12/Mon.Aug.13
19:01
20:10
4:44
5:52
N/A
20:31
6
11 21.5
7 23


Forecast issued by: Ryan Lyman
Contact Us - (808) 932-2323
Hours: Mon-Fri 8 AM - 5 PM HST (1800-0300 UTC)

For public road conditions and snow report message please call (808) 935-6268.
This message is also available at the MKWC road conditions page.

Next update at 5 PM HST Wednesday 08 August (0300 UTC Thursday 9 August) 2018.
Please call or email to be placed on the Mauna Kea Weather Bulletin email list.