July 17th, 2009

July 22 Great Solar Eclipse PFS Bulletin No. 11

Published at 0:33. Filed under Precision Forecast Service; no comment so far.

EDITIONAL NOTICE

This bulletin is revised at July 16 1730 UTC, missed tropical cyclone information is added, and the precision forecast map comes online.

OVERVIEW

This is July 22 Great Solar Eclipse PFS Bulletin No. 11, issued in both English and Chinese. The forecast reasoning has slightly changed since previous bulletin. There is only 6 days away from the event. The uncertainty for this forecast is upgraded to very small. The forecast diagrams mentioned below may be found at http://7timer.y234.cn/V3/product.php?language=en&product_id=2 and https://www.fnmoc.navy.mil. Precision numeric forecast for various locations may be found at http://7timer.y234.cn/V3/product.php?language=en&product_id=1. RSS feed of this service is available at http://7timer.y234.cn/V3/wordpress/?feed=rss2&cat=46.

ANALYSIS

NCEP GFS JUL16/00Z's forecast on 500hPa geopotential heights of JUL22/00Z revealed a weak subtropical high over western Pacific with an oblique ridge. An animation with nearby taus shows the subtropical high is weakening, with 5880gpm contour stays east of 140E at JUL22/00Z, but a weak splitted  high can still be spotted by 500hPa streamlines of JUL22/00Z although no contour is shown on the geopotential heights. On the other hand, a westerly trough is locating over Central China, and a 850hPa shearline is lifting over the Yellow Sea and Jiangsu Province (around 120E 34N). The position and the intensity of the Arabian Sea subtropical high did not suffer a major change since last run. Meanwhile, forecast for 300hPa geopotential heights revealed that the ridge of Qinghai-Xizang anticyclone locates south of 30N.

ECMWF JUL16/00Z's forecast on 500hPa geopotential heights of JUL22/00Z has retracted the claim of a strong western Pacific subtropical high to be persisted around July 22. Its situation is similar to NCEP GFS's now although the intensity of the subtropical high is still higher than the later's, with the 5880gpm contour reach west of 140E and a splitted subtropical high locates over Taiwan (as noted above, this splitted high does also appeared on GFS's forecast for JUL21/12Z for an intensity of over 5880gpm but not for JUL22/00Z). Weak 850hPa shearline is still suggested over southern Jiangsu Province with no 500hPa westerly trough visible, while the monsoon over India persisted.

FNMOC NOGAPS JUL16/00Z's forecast on 500hPa geopotential heights of JUL22/00Z also depicts a weak western Pacific subtropical high, the intensity is weaker than GFS or ECMWF suggest, with 5880gpm contour east of 150E. 500hPa streamlines analyses show a weak ridge over Ryukyu Islands extending to Central China. On the other hand, an area of 850hPa positive relative vorticity can be spotted over Jiangsu Province, an associated shearline is visible on 850hPa and 700hPa streamlines analyses. The main body of Arabian Sea subtropical high locates in Saudi Arabia, with a weaker intensity comparing with GFS's forecast. Monsoon over southern India is persisted. Forecast for 300hPa geopotential heights revealed a ridge of Qinghai-Xizang anticyclone locates south of 30N, which is consistent with GFS's.

For analyses of three well-known numeric models above, we can now depict:

1. Western Pacific subtropical high is likely to be weaker than long term mean (for a long term mean graph, please refer to bulletin No. 6), all three models have depicted a highly similar result on this conclusion. A southward Qinghai-Xizang anticyclone ridge and a development of El Niño event also suggest a similar trend. However, the models have also suggested a splitted high or a weak ridge is possible to turn up around East China Sea.
2. A low level shearline can be located around 115E 33N (i.e. in Jiangsu Province), this is also suggested by all three models. The intensity of this shearline remains in question but shall not be strong. There is also a chance for a drifted southwest vortex located over Central China (suggested by GFS).
3. India Peninsula is unlikely to be controlled by the Arabian Sea subtropical high, but a monsoon will run in at that time.

The uncertainty for this forecast is upgraded to very small as the results from all three models are consistent.

By July 16 at 18Z, tropical storm Molave (07W) locates over east of Luzon and is expected to move into South China Sea in the coming days. It is likely that Molave will affect the weather of July 22.

FORECAST

The forecast is much more pessimistic than the previous bulletin since ECMWF and NOGAPS have both retract their expectation of normal-to-strong western Pacific subtropical high. The uncertainty has reduced since there is no significant divergence between the models. Local forecasts are listed below. Please be aware that these forecasts may change as there is still 6 days to go for the event.

• In India: mainly cloudy over most totality area but may have more sunshine over east (suggested by GFS). Showers are likely during the day. 
• In Sichuan and Chongqing, China: cloudy to overcast, may have a few sunshines. FNMOC EFS suggests a precipitation probability of >90% on the mountainous area west of Chengdu, but for Chengdu-Chongqing plain the probability is less than 10%. However, GFS proposes a possibility of heavy rain at Sichuan Basin produced by the developed southwest vortex.
• Around Wuhan, China: cloudy to overcast with precipitation probability of >40% according to EFS.
• Around Tongling, China: cloudy to overcast with precipitation probability of >50% according to EFS.
• Pan-Yangtze River Delta, China: cloudy to overcast. 
• Ryukyu Islands, Japan: cloudy as the subtropical high is weak.

The 12km MM5/GFS model is coming online and it is now under test, initialization for this run is at JUL14/18Z. Eclipse map produced by Occult 4 has been combined with the cloud cover graph. Please download the KML file and open it with Google Earth (http://earth.google.com/). The forecast time is July 22 from 0100 UTC to 0400 UTC with 1-hour interval, the forecast region includes most of totality area over China. Warning: by reading this message you have acknowledged that this is a service that still under test! My experience is that sometimes it is not better than the original GFS, although resolution of the later is much lower than this service. For GFS forecast maps, please refer to http://7timer.y234.cn/V3/product.php?language=en&product_id=2.

Download the KML file

NEXT UPDATE

July 17 at 1500 UTC or earlier.