MM5 Simulation of Hurricane Diana Genesis

In a key step toward improving the prediction of hurricanes, NCAR scientists have reproduced in a computer model the fine-scale structure that drives the birth and strengthening of tropical cyclones. The simulation marks the first time a cloud-resolving simulation has been able to reproduce the formation of a tropical cyclone, given only information about atmospheric conditions on a scale much larger than that of the cyclone.

To resolve the eyewall and precipitation bands within a tropical cyclone, the MM5 model was used. With a horizontal distance as small as 1.2 km between the model's computation points, MM5 is one of the world's highest-resolution models for reproducing storm-scale weather across a large area. Diana was chosen because of ample surface data and because a well-defined nontropical low preceded its formation.

Rainwater at .65g/kg is shown as a yellow isosurface and Cloudwater at .35g/kg is shown in white. Because of the course time resolution, the structures jump around a lot, but the clear definition of the eye just off the coast is visible at the end of the time sequence which is 49 hours long.