How to sync offline HTML5 webdatabase with centralised database

I'd like to be able to do the following in a HTML5 (iPad) web app:

• upload data to an online database (which would be probably <50Mb in size if I was to build the online database in something like SQLite)
• extract either a subset or a full copy of data to an offline webdatabase
• (travel out of 3G network coverage range)
• perform a bunch of analytic-type calculations on the downloaded data
• save parameters for my calculations to the offline webdatabase
• repeat, saving different parameter sets for several different offline analytic-type calculation sessions over an extended period
• (head back into areas with 3G network coverage)
• sync the saved parameters from my offline webdatabase to the central, online database

I'm comfortable with every step up till the last one...

I'm trying to find information on whether it's possible to sync an offline webdatabase with a central database, but can't find anything covering the topic. Is it possible to do this? If so, could you please supply link/s to information on it, OR describe how it would work in enough detail to implement it for my specific app?

Thanks in advance