Sometime there’s nothing one can do to prevent poor site performance. Such was the case when Hurricane Sandy hit the East Coast. New York, one of the hardest hit areas by the storm, is one of the two locations where mobile and web performance management firm Keynote Systems Inc. measures the performance of the 30 retailers on the Keynote Mobile Commerce Performance Index.

“Hurricane Sandy caused 25% of cell towers, as reported by telecommunications companies, to go dark and disrupt service in many areas of the Northeast, and all retailers on the index had significant availability issues from areas impacted by Sandy,” says Haroon Chohan, mobile and web performance expert at Keynote Systems. “There were a significant number of page loading failures from our New York mobile monitoring location due to service unavailability issues. There is really no way to protect yourself from outages caused by natural disasters. If the data center is impacted, traffic can be re-routed to another data center. But if cell service is not available, your users are not going to be able to get to your site.”

The average success rate—the percentage of the time a mobile commerce site can be loaded completely and successfully—for all 30 retailers on the index for the week ending Nov. 4 was 99.17%, down from 99.19% the previous week, a move that can negatively impact mobile conversion rates, Keynote Systems says. Many requests for the m-commerce sites were being met with connection errors because of the effects of the storm on cell towers, Keynote explains. The average page load time on the index was 9.45 seconds. Weighting and combining the load time and success rate provides an index average score of 654 out of 1,000.

Amazon.com Inc. topped the index with an average page load time of 5.88 seconds and a success rate of 99.88% for a score of 928. Barnes & Noble came in second with a load time of 6.04 seconds and a success rate of 99.88% for a score of 922 out of 1,000. And HSN Inc. came in third with a load time of 6.84 seconds and a success rate of 99.88% for a score of 897.

Click here and then click on Keynote Mobile Commerce Performance Index Part 1 and Part 2 to see this week’s complete results for all 30 retailers on the index.

Keynote Systems measures 30 representative m-commerce sites exclusively for Internet Retailer. The sites include merchants in multiple categories and channels, and of multiple sizes, ranging from such giants as Amazon.com Inc. to midsized retailers like Toolfetch.com LLC. Amazon is No. 1 in the Internet Retailer Mobile 400, Toolfetch.com is No. 248. Keynote tests the sites in the index every hour Monday through Sunday from 8 a.m. through midnight Eastern time, emulating three different smartphones on three different wireless networks: Apple Inc.’s iPhone 4 on AT&T, the HTC Evo on Sprint and the Droid X on Verizon. The HTC Evo and the Droid X run Google Inc.’s Android operating system. Keynote runs the tests in New York and San Francisco.

Keynote combines a site’s load time and success rate, equally weighted, into a single score. Given that both performance and availability are important, the score reflects the overall quality of the home page; a higher score indicates better performance. Scores also reflect how close sites are to one another in overall quality. The index average score is the midpoint among all the sites’ scores.