Warnings Wind, rain, and fog expected tonight. Very good chance for thunderstorms and electrical activity. Cloud Cover and Precipitation Forecast The inversion is expected to weaken through this afternoon and will be gone from then through tomorrow evening. Instead it will be replaced with a saturated environment. As a result, very moist, cloudy, and rainy conditions are expected at the summit during this period. Thunderstorms are also very likely mostly for tonight through tomorrow morning. However, an occasional rumble is possible late tomorrow afternoon. The inversion is then slated to slowly rebuild late tomorrow night, becoming very well-defined by Tuesday. Thus, more intermittent periods of fog is very likely Tuesday morning giving way to dry air for Tuesday night. The cirrus along the fringes of Hurricane Jimena should already be visible from the summit at this time, and is expected to be over the summit within the next 2 to 3 hours. The skies will only get worse as the clouds thicken through the night with Jimena's passage. This will make for 100% cloud cover for tonight. Jimena is expected to pass to the south of the Islands later tonight, but will continue to produce lots of high clouds as it marches westward over the next 3 to 5 days. The high clouds from Jimena will be pulled up with the weak southwesterly winds aloft and pass over the summit through tomorrow night. These clouds are then expected to linger to the west of the summit for Tuesday night. As a result, cloud cover will likely drop to 60 to 80% for tomorrow night and around 30 to 50% for Tuesday night. Summary of Key Meteorological Variables See table below. Discussion Very poor conditions expected at the summit for the next two nights. Hurricane Jimena, now about 350 km east-southeast of Hilo, is currently moving due west at about 17 mph. It is projected to pass around 100 km south of the Big Island sometime tonight/tomorrow morning. This close passage to the Big Island will make for saturated, unstable, cloudy, and rather windy conditions at the summit tonight through most of tomorrow night. The intensity of Jimena is not expected to change much as it passes our longitude, despite being influenced by some minor shear aloft. Rainbands along its northern periphery will likely produce thunderstorms and rain at the summit for much of tonight. Residual moisture/instability combined with southeasterly winds tomorrow may help produce more isolated thunderstorms tomorrow afternoon. But once Jimena moves well west of the Big Island, the tradewind inversion is expected to slowly rebuild, paving the way for dry conditions on Tuesday night. However, the high clouds from Jimena will likely linger to the west of the Big Island for that night. For more information on Hurricane Jimena, please read the latest forecast and discussion issued by the Central Pacific Hurricane Center. Astronomical Observing Quality Guidance Vertical Profiles from MM5 (vertical coordinate is pressure in mb): 2 pm HST Sun 31 Aug (0000 UTC Mon 01 Sep) Seeing Cn2 5 pm HST Sun 31 Aug (0300 UTC Mon 01 Sep) Seeing Cn2 8 pm HST Sun 31 Aug (0600 UTC Mon 01 Sep) Seeing Cn2 11 pm HST Sun 31 Aug (0900 UTC Mon 01 Sep) Seeing Cn2 2 am HST Mon 01 Sep (1200 UTC Mon 01 Sep) Seeing Cn2 5 am HST Mon 01 Sep (1500 UTC Mon 01 Sep) Seeing Cn2 8 am HST Mon 01 Sep (1800 UTC Mon 01 Sep) Seeing Cn2 Tonight's (Sunday Night) Collage Seeing Cn2 Tuesday Night's Collage (available after 0800 HST on Tuesday) Seeing Cn2 Wednesday Night's Collage (available after 0800 HST on Wednesday) Seeing Cn2

3-day Forecast Summary (Latest GFS Trend)	2 pm HST Sun 31 Aug	8 pm HST Sun 31 Aug	2 am HST Mon 01 Sep	2 pm HST Mon 01 Sep	8 pm HST Mon 01 Sep	2 am HST Tue 02 Sep	2 pm HST Tue 02 Sep	8 pm HST Tue 02 Sep	2 am HST Wed 03 Sep
	0000 UTC Mon 01 Sep	0600 UTC Mon 01 Sep	1200 UTC Mon 01 Sep	0000 UTC Tue 02 Sep	0600 UTC Tue 02 Sep	1200 UTC Tue 02 Sep	0000 UTC Wed 03 Sep	0600 UTC Wed 03 Sep	1200 UTC Wed 03 Sep
PW (mm, summit upward)	4 to 6	8 to 12	8 to 12	8 to 12	6 to 8	5 to 7	2 to 3	2 to 3	2 to 3
Summit Temp (oC)	8	2	2	5	2.5	3	10	5.5	5
Wind Dir/Speed (mph)     Summit     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/20 to 30 E/17 SE/17 SSE/22 SSE/19 S/13 SSW/16 ESE/16	ENE/35 to 50 E/23 E/13 SE/12 SE/21 SE/26 SSE/14 SE/16	E/40 to 60 ENE/30 ENE/23 ESE/17 SE/18 SSE/18 S/17 ESE/19	ESE/25 to 40 ESE/17 E/22 E/19 SE/15 S/14 S/7 ESE/19	E/20 to 30 E/19 ESE/26 E/24 ESE/13 S/3 NE/1 ENE/19	ENE/15 to 25 ESE/15 SE/22 ESE/17 SE/6 N/6 NNE/12 E/21	E/15 to 25 E/14 ESE/13 ESE/8 ENE/4 NNE/14 NE/14 E/18	E/15 to 25 E/15 ESE/10 ENE/7 NE/6 NE/14 ENE/12 ENE/18	E/15 to 25 E/13 ESE/8 NE/3 NNE/7 N/15 NE/11 ENE/17

Night (HST)	Sun Set	Twilight End	Twilight Beg	Sun Rise	Moon Rise	Moon Set	Illum (%)	RA	Dec
Sun.Aug.31/Mon.Sep.01	18:47	19:53	4:52	5:57	N/A	22:00	26	14 31.2	-14 12
Mon.Sep.01/Tue.Sep.02	18:46	19:52	4:52	5:58	N/A	22:45	37	15 26.5	-19 23
Tue.Sep.02/Wed.Sep.03	18:45	19:51	4:52	5:58	N/A	23:35	48	16 24.7	-23 29

Forecast issued by: Ryan Lyman
rlyman@hawaii.edu
(808) 932-2323

Next update at 10 am HST Tuesday 02 September (2000 UTC Tuesday 02 September) 2003.
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This page was last modified on: Wed, Apr 22 2009 - 2058 UTC
Send comments to: Ryan Lyman