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Numerical experiments are performed with the fifth generation Mesoscale Model to study the evolution of island airflow, thermodynamic fields, and clouds over the island of Hawaii at night. The model has successfully simulated the major observed features associated with the nocturnal flow regime. These include the formation of nocturnal inversion, development, gradual offshore extension and deepening of the katabatic flow, shifting of the overall cloudy areas from the windward slopes to the ocean, and generation of clouds within the simulated offshore convergence zone. Furthermore, it is also shown that rain evaporative cooling affects the depth, strength, and offshore extension of the katabatic flow. In the early evening, the nocturnal cooling provides the land–sea thermal contrasts for the development of the simulated downslope flow on the windward slopes. With continued nocturnal cooling and rain evaporation, the simulated katabatic flow extends toward the coast. The simulated convergence zone ...

Initialized by the composite upstream sounding during the Hawaiian Rainband Project, high-resolution numerical experiments are conducted using the Pennsylvania State University–National Center for Atmospheric Research fifth generation Mesoscale Model to study the island-scale airflow and cloud distributions over the island of Hawaii without considering the diurnal heating cycle. The observed mean patterns of island airflow and weather under the summer trade wind conditions are well simulated. These features include orographic clouds on the windward slopes, flow deceleration and splitting on the windward side, leeside vortices, and cool and moist (warm and dry) conditions on the windward (lee) side. In addition to Fr (Froude number), the simulated island airflow and cloud distributions are sensitive to net diabatic heating associated with clouds and precipitation and rain evaporative cooling. The trade wind inversion height determines the depth of the moist trade wind layer, which also affects the...

The data collected on 10 August 1990 from the Hawaiian Rainband Project were analyzed to study the evolution of katabatic flow. Results from this study show that for a relatively dry case thermal forcing is important to account for the onset, evolution, depth, and offshore extension of the katabatic flow on the windward side of the island of Hawaii where the mean winds are weak because of island blocking. During the evening transition, the initiation of katabatic flow on the windward slopes was mainly driven by the diurnal heating cycle. At the windward coast, the wind shift was caused by the arrival of the drainage front from the windward lowlands. After the arrival of the drainage front at Hilo, slopewise instability was generated because of rain showers along the coast and diminishing orographic clouds and showers on the slopes. Along the coast, because of the reduced radiative cooling due to cloud cover and vertical mixing associated with rains, a warm period was observed at Hilo. On the slop...

Both the daily rainfall on the windward side of the island of Hawaii and the early morning (0200 HST—Hawaiian standard time) trade-wind inversion height at Hilo varied substantially during the Hawaiian Rainband Project (HaRP). In general, the inversion was higher during the passage of a cold front to the north or during the approach of tropical disturbances from the east to the south. The daily rainfall on the windward side is highly correlated with the 0200 HST inversion height at Hilo with a maximum correlation greater than 0.7 in the Hilo area. The daily daytime (1100–1900 HST) rainfall on the windward slopes, nocturnal (1900–0300 RST) showers an the windward lowland, and coastal precipitation in the predawn and early morning hours (0300–1100 HST) are also highly correlated with the inversion height with a maximum correlation greater than 0.7, 0.7, and 0.5, respectively. For the low- (high-) inversion days, the median daily rainfall on the windward side is about one-half (more than twice) of t...