The water budget of a hurricane as dependent on its movement

TL;DR

This study reveals that hurricanes primarily consume pre-existing atmospheric moisture along their path, with their movement velocity determining their water vapor budget, challenging the traditional focus on local evaporation as the main moisture source.

Contribution

It introduces a new perspective that hurricane rainfall depends on the storm's movement and pre-existing atmospheric moisture, not just local evaporation, extending analysis to 3000 km from the storm center.

Findings

Hurricanes do not rely solely on local evaporation for rainfall.

The storm's movement velocity influences its water vapor intake.

Hurricanes create a dry wake reducing rainfall by up to 40%.

Abstract

Despite the dangers associated with tropical cyclones and their rainfall, the origins of storm moisture remains unclear. Existing studies have focused on the region 40-400 km from the cyclone center. It is known that the rainfall within this area cannot be explained by local processes alone but requires imported moisture. Nonetheless, the dynamics of this imported moisture appears unknown. Here, considering a region up to three thousand kilometers from storm center, we analyze precipitation, atmospheric moisture and movement velocities for North Atlantic hurricanes. Our findings indicate that even over such large areas a hurricane's rainfall cannot be accounted for by concurrent evaporation. We propose instead that a hurricane consumes pre-existing atmospheric water vapor as it moves. The propagation velocity of the cyclone, i.e. the difference between its movement velocity and the mean velocity of the surrounding air (steering flow), determines the water vapor budget. Water vapor available to the hurricane through its movement makes the hurricane self-sufficient at about 700 km from the hurricane center obviating the need to concentrate moisture from greater distances. Such hurricanes leave a dry wake, whereby rainfall is suppressed by up to 40 per cent compared to its long-term mean. The inner radius of this dry footprint approximately coincides with the radius of hurricane self-sufficiency with respect to water vapor. We discuss how Carnot efficiency considerations do not constrain the power of such open systems that deplete the pre-existing moisture. Our findings emphasize the incompletely understood role and importance of atmospheric moisture supplies, condensation and precipitation in hurricane dynamics.