July 15th, 2009

July 22 Great Solar Eclipse PFS Bulletin No. 10

Published at 10:36. Filed under Precision Forecast Service; 4 Comments

OVERVIEW

This is July 22 Great Solar Eclipse PFS Bulletin No. 10, issued in both English and Chinese. The forecast reasoning has slightly changed since previous bulletin. Although there is only 7 days away from the event, the divergent results given by difference models make the uncertainty for this forecast remains moderate. The GFS forecast diagrams mentioned below may be found at http://7timer.y234.cn/V3/product.php?language=en&product_id=2. Precision numeric forecast for various locations may be found at http://7timer.y234.cn/V3/product.php?language=en&product_id=1.

ANALYSIS

GFS JUL14/18Z's forecast on 500hPa geopotential height of JUL22/00Z revealed a weak subtropical high in western Pacific. On the other hand, there is an northeast vortex over Northeast China, with a 850hPa shearline over northern Bohai Sea, but there is no significant westerly trough over North China. The position and the intensity of the Arabian Sea subtropical high did not suffer a major change since last run. In all, the positions of the major systems had not been revised significantly but instead of their intensities. Meanwhile, the ridge of Qinghai-Xizang high is near 30N as spotted from 100hPa geopotential height diagram, which is nearly the same as that of last run.

ECMWF JUL14/12Z's forecast on 500hPa geopotential height of JUL22/00Z still suggested a strong western Pacific subtropical high with its 5880gpm contour reach 110E. A weak 850hPa shearline is purposed around Bohai Sea with no 500hPa westerly trough visible, while the monsoon over India persisted.

FNMOC NOGAPS JUL14/12Z's forecast on 500hPa streamlines suggested a situation similar to ECMWF's, with a splitted subtropical high centred around Wuhan. Again, no significant westerly trough can be seen around North China; but FNMOC EFS JUL14/12Z's forecast on 5640gpm contour probability of JUL21/12Z suggested a deeper-than-usual East Asia Major Trough with 90% probability that the 5640gpm to be located near 45N, and this is consistent with what GFS suggested.

By July 15 at 00Z, good disturbance 91W is activing over west of Palau while poor disturbance 94W is centred over northern South China Sea, but the probability for them to affect the weather of July 22 is low. However, we shall note that NOGAPS did suggest two weak tropical cyclones activing over western Pacific Ocean around July 22.

FORECAST

The divergent results available make it difficult to figure a confident prediction. It is encouraging to see both ECMWF and NOGAPS have suggest something promising. Local forecasts are listed below. Please be aware that they are rough due to the moderate uncertainty of enviromental forecast and may suffer major changes.

• In India: cloudy and rainy over most totality area as a monsoon run in. May be have some sunshine over Patna and further east. 
• In Sichuan and Chongqing, China: overcast and rainy as a southwest vortex is centred over Sichuan Basin according to GFS; but can be partly clear if ECMWF and NOGAPS get it right. 
• Around Wuhan, China: shall be cloudy with showers according to GFS, but can be mostly clear according to ECMWF and NOGAPS.
• Pan-Yangtze River Delta, China: situation close to Wuhan. 
• Ryukyu Islands, Japan: shall be cloudy with a few heavy showers according to GFS, but can be mostly to partly clear according to ECMWF and NOGAPS.

NEXT UPDATE

July 16 at 1500 UTC or earlier. Precision forecast for mainland China with a resolution up to 12km might be available for test by that time.

ACKNOWLEDGEMENT

I would like to thank President Dickson Fu from Sky Observers' Association (Hong Kong) for his valuable contribution to this work.