The Effect of Hawai’i’s Big Island on Track and Structure of Tropical Cyclones Passing to the South and West*

The effect of the Big Island of Hawai’i on tropical cyclone (TC) track and structure is investigated using the Weather Research and Forecasting (WRF) model. The high (;4000 m) mountains of the Big Island modulate lower-tropospheric flow in such a way that it can influence TCs hundreds of kilometers away from the island. When a TC approaches from the east, the blocking of lower-tropospheric flow leads to a slowing of the TC’s movement. As a TC passes close to the south side of the Big Island, it deviates southward. The TC core convection and winds can become axisymmetric because of the blocking of the stronger northeasterly flow to the north of the storm. The authors hypothesize that this axisymmetrization led to the unexpected eye formation of Hurricane Flossie (2007) just southeast of the Big Island. As a TC moves into the lee (southwest side) of the Big Island, the flow associated with the island wake leads to a track deviated to the right. The Hurricane Dot (1959) simulations suggest that this effect contributed to an observed deviation to the north, which led to eventual Kauai landfall. A greater TC intensity is found in the lee of the Big Island compared to the case without the island, which is primarily attributed to a weakened vertical wind shear associated with the island blocking.