In order to operate large telescope, it is crucial to have a good weather forecast especially of the temperature when the telescope begins preparation, i.e., open the dome to introduce new fresh air inside. For this purpose, the Mauna Kea Weather Center (MKWC) has been established in July 1998 by the initiative of Institute of Astronomy, University of Hawaii. The weather forecast is not a simple matter and is difficult in general especially as in the quite unique environment as in the summit of Mauna Kea. MKWC introduced a system of numerical forecasting based on the mesoscale model, version five, so called MM5, was running on the vector parallel super computer VPP700 of Subaru Telescope for past three years. By the introduction of new supercomputer system at Subaru Telescope, we have prepared new programs for the new supercomputer systems. The long term but coarse grid forecast is available through National Center for Environmental Predict (NCEP) every day, and the MKWC system get the result of simulations on coarse grid over the pacific ocean from NCEP, and readjustment of data to the fine grid down to 1km spatial separation at the summit of Mauna Kea, i.e. Telescope sites of Mauna Kea Observatories. Computation begins around 20:00 HST, to end 48 hours forecast around 0100am next morning. Conversion to WWW graphics will finish around 0500am, then, the specialist of MKWC would take into the result of the numerical forecast account, to launch a precious forecast for the all observatories at the summit of Mauna Kea, at 10:00am HST. This is the collaboration among observatories to find a better observation environment.