HYSPLIT 4.9 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. This free program is a product of Air Resources Laboratory.
We cannot guarantee that the program is safe to download as it will be downloaded from the developer's website. Before launching the program, check it with any free antivirus software. The program is included in Education Tools. The most popular versions among the software users are 4.9 and 1.0.
From the developer:
The HYSPLIT (HYbrid Single-Particle Lagrangian Integrated Trajectory) model is a complete system for computing simple air parcel trajectories to complex dispersion and deposition simulations. The intial development was a result of a joint effort between NOAA and Australia's Bureau of Meteorology. Recent upgrades include enhancements provided by a number of different contributors.
You may want to check out more software, such as StatPlus 2007, GenScn or Flashcard Tables, which might be related to HYSPLIT.