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Using 1979–2003 radiosonde data at Hilo and Līhu‘e, Hawaii, the trade wind inversion (TWI) is found to occur approximately 82% of the time at each station, with average base heights of 2225 m (781.9 hPa) for Hilo and 2076 m (798.8 hPa) for Līhu‘e. A diurnal pattern in base height of nighttime high and afternoon low is consistently found during summer at Hilo. Inversion base height has a September maximum and a secondary maximum in April. Frequency of inversion occurrence was found to be higher during winters and lower during summers of El Niño years than non–El Niño years. Significant upward trends were found for inversion frequency at Hilo for March–May (MAM), June–August (JJA), and September–November (SON) seasons, and at Līhu‘e for all seasons and for annual values.