Forecast for the Total Solar Eclipse on July 22, 2009

By: Dr. Rob Carver , 10:40 AM GMT on July 21, 2009

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A total solar eclipse is going to occur over Asia, moving eastwards towards and across the Pacific Ocean around 0000 GMT on July 22. Here's the path of totality according to NASA

Figure 1. Plot of totality (Dark blue circles) and partial eclipse coverage (aqua line) from NASA

There's one catch about this particular eclipse, it's over the tropics in summer. Now if you're planning a field campaign to study tropical cirrus from thunderstorm anvils, this is the ideal season and location. But if you're trying to look at the eclipse (using eyesafe techniques!) from the ground, these high clouds can be a problem. In fact, NASA made this plot of average cloudiness to illustrate the point.

Figure 2. Plot of average cloud cover around the eclipse path from NASA

However, this is only a climatology based on observations. What's the forecast? Well, here's the GFS forecast of MSL pressure and precipitation valid for 00Z July 22, 2008

Figure 3. GFS forecast of MSL pressure and precipitation for 00Z July 22

Why am I looking at forecast precipitation instead of forecast cloud cover? Well, the GFS is a global model and isn't the best choice to represent the evolution of high clouds that are the result of thunderstorms. Instead, I'm using the model to assess where convection is likely and use my judgement as to how much cloud cover will be present.

With that in mind, here's the forecast for cloud coverage along the eclipse track. Apologies to my readers in China, I don't know the proper province names.

India NE into Tibet/China: +50% chance of high clouds obscuring the eclipse.

China just east of the Tibetan plateau: Might actually be clear viewing of the eclipse

Rest of the eclipse path east to Shanghai: +70% chance of high clouds or actual storms blocking the view. The subtropical jet is just along the eclipse path here and it's providing dynamic forcing for storms

From Shanghai east through the Ryushu islands of Japan: +70% chance of clouds and/or storms. The subtropical jet is here as well.

Iwo Jima and neighboring islands: Looks like good viewing. The subtropical jet pulls to the North, carrying the clouds away, and stray clouds from the Inter Tropical Convergence Zone (ITCZ) are to the east.

Enewetak Atoll: The GFS is indicating scattered thunderstorms in a broad area just including and to the east of this atoll. Based on previous satellite imagery and the clearing of storms to the west, I'm predicting +30% chance of high clouds obscuring the eclipse.

The Kiribati islands: +50% chance of obscured viewing. These islands are in the heart of the ITCZ and the GFS is indicating more extensive thunderstorm coverage than for Enewetak.

If you're lucky enough to be in a place to see this eclipse, be sure to take a few photos and share them with everybody using WunderPhotos.

Note: For more information about this eclipse and to see where I obtained the eclipse graphics, visit

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2. Spetrm
1:30 PM GMT on July 21, 2009
Nice forecast, way to use the GFS, good call!
Member Since: June 9, 2007 Posts: 410 Comments: 9857
1. Tazmanian
1:12 PM GMT on July 21, 2009
well ca see this???
Member Since: May 21, 2006 Posts: 5091 Comments: 115454

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About rcarver

Rob is the Research and Development Scientist for Weather Underground. He has a Ph.D. in meteorology from Penn State University.

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