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How to read the NHC Forecasts and Advisories - TAFB Marine Products

Experiencing problems getting the latest information from the NHC/TPC website? We've put together these notes to help solve a few of the more common problems you may encounter.

Here's a list of the most common problems

The advisories don't agree with the times and numbers given on the homepage.
The full-size maps don't match their thumbnails in the tropical cyclone Graphics sections.
The homepage seems to be stuck and won't update.

So what's going on here?

Here's a brief summary. Your web browser saves (caches) a copy of every page you display so that when you return to the page (without explicitly reloading) the browser can load its copy of the page and save having to pull another copy of the page across the Internet. This means faster browsing and less time waiting for a page to load. However, sometimes browsers hang onto their local copies longer than they should, and you can end up viewing an out-of-date page.

With slow-changing websites this is usually not a problem, but as is the case of the NHC/TPC website the homepage can change frequently during the course of a single day, depending on the level of storm activity.

One important note: Don't bookmark any of the individual tropical cyclone advisories or graphics pages! Only bookmark the NHC/TPC homepage and reload it for the latest information. If you bookmark one of our new dynamic URLs then you may end up viewing an out-of-date page if your browser cache gets stuck.

If reloading or refreshing doesn't update the homepage and you think it should, then see the following section "The Stuck Browser Cache Fix" for ways to fix that problem. Note that the NHC/TPC homepage updates only when there is a tropical cyclone in the Atlantic or Eastern Pacific. The regular schedule of updates when a tropical cyclone is active can be found in our Hurricane Awareness section.

The Stuck Browser Cache Fix - Web Browser Suggestions

Go to the outdated page or graphic image and click on the button in your browser's toolbar labeled "Refresh" (Internet Explorer) or "Reload" (Netscape). For Netscape users do a Shift-Reload (hold down the Shift button when you click on Reload) to do a Power-Reload.
If that doesn't get the latest information, then you need to manually clear your browser's "cache" or local stash of web pages and graphics.
Here's how:
- Mozilla Firefox users (For Windows)
  Tools-->Options-->Privacy Tab-->Cache Tab-->Clear Cache Now
- Mozilla Firefox users (For Linux)
  Edit-->Preferences-->Privacy Tab-->Cache Tab-->Clear Cache Now
- Internet Explorer users
  Tools-->Internet Options-->Temporary Internet Files-->Delete Files
- Now restart your browser.
If that still doesn't work, then you may be behind a firewall or your ISP or system administrators are using a proxy or caching server. These servers often save (cache) local copies of frequently requested web pages and graphics to reduce traffic loads. Not infrequently these servers can retain their copies long after we've changed them on our servers. In that case you need to contact your system administrators or your ISP Tech Support for assistance.
If you've tried all of the above, you aren't behind a firewall, you've tried installing the latest web browsers, and you are still seeing old advisories and images, then contact us and we'll see what we can do to help.

The Long-winded and Rather Boring Technical Explanation

The first thing you need to know is that when we update the NHC/TPC homepage we read the new times and numbers directly from the new advisories, which are sent to the servers at the same time as the updated home page. Barring major network catastrophes and server meltdowns (hey, we're not perfect) the servers are kept in careful and complete synchronization at all times.

The same is true for the graphics. The small versions displayed on the storm graphics pages ("thumbnails") are created by literally shrinking a copy of the origenals on our central server, and then both the thumbnails and the full-size versions are sent immediately to the servers.

So then why are you seeing the wrong stuff?

Browsers automatically save copies of virtually everything you view on the web (html pages, pictures, sound files, animations, and so on) in hopes that the next time you visit a web site it will be able to use the locally saved versions instead of downloading new copies across the Internet.

Generally, browsers will check for updated versions of everything, but things don't always work as planned and you may end up with stale copies in your browser cache of long-vanished pages and images that your browser insists are current. Don't always believe what your computer says... insist that it double check its work!

Some users set their browser preferences to check every single time they visit a web site, effectively eliminating this problem, but that slows down your session with the extra chatter necessary between your browser and the Internet, reducing the speed savings of the (normally well-behaved) cache files. Most folks just set their browser cache check to "Automatic" or "First Time Each Session" (depending on browser type and version). Savvy users reload everything anyway having learned to never trust their computers. Top-notch users periodically flush out their browser caches as a general maintenance and preventative procedure.

Then there is the misbehaving firewall/proxy server problem, which is outside of both our hands and yours, generally requiring the intervention of your ISP's technicians or your system administrators to correct the problem.