Pam formed on March 6, east of the Solomon Islands and tracked slowly in a generally southward direction, slowly intensifying as it did so. Two days later, the disturbance reached tropical cyclone intensity and, over subsequent days, Pam gradually strengthened before reaching Category 5 cyclone status on both the Australian and Saffir–Simpson scales on March 12. The next day, Pam's sustained winds peaked at 250 km/h (155 mph) as the storm moved through Vanuatu, passing near several constituent islands and making direct hits on others. On March 14, Pam's winds began to slowly weaken, but its pressure dropped further to a minimum of 896 mbar (hPa; 26.46 inHg) before rising shortly afterwards. Over the next few days, the cyclone's weakening accelerated as it moved poleward. On March 15, Pam passed northeast of New Zealand before transitioning into an extratropical cyclone that same day.
Early in Pam's history, a damaging storm surge was felt in Tuvalu, forcing a state of emergency declaration after 45 percent of the nation's residents were displaced. Torrential rainfall occurred in the southeastern Solomon Islands, particularly in the Santa Cruz Islands. In Vanuatu, all emergency centers were activated and relief personnel were put on standby with Pam assessed as having the potential to be one of the nation's worst tropical cyclones. Catastrophic damage occurred as the storm moved through the archipelago, particularly in Efate, location of the Ni-Vanuatu capital of Port Vila; and the Tafea islands of Erromango and Tanna. The cyclone crippled Vanuatu's infrastructure: an estimated 90 percent of the nation's buildings were impacted by the storm's effects, telecommunications were paralyzed, and water shortages continue to plague the small nation. Pam later brought heavy winds and rough surf to New Zealand's North Island during its weakening stages.