The recent extremely powerful Hurricane Patricia off the west coast of Mexico, the most intense hurricane ever measured in the Western Hemisphere, was noteworthy for a number of reasons.
Perhaps primarily, it was characterized by the incredible fact that its central minimum pressure decreased by 100 millibars in 24 hours from Oct. 22-23. Since the average sea-level pressure is just over 1,000 millibars, that means that 10 percent of the atmospheric column over the center of Patricia was somehow evacuated in only one day.
This mass evacuation is accomplished by upward vertical motion of the air and subsequent exportation to locations far from the central core of the storm. The circumstances that promote these vertical motions and allow the exportation of the air that is lifted are complicated and difficult to anticipate in extreme cases like Patricia.
However, the very same upward vertical motion and exportation of air occurs in the center of mid-latitude storms such as the ones that bring us our winter snows or even the one that brought us a rainy Halloween. A typical rate of intensification for a robust snowstorm such as those we might receive in Madison during winter is 12 millibars of pressure fall per day — more than eight times less dramatic than that which characterized Patricia.
Such sudden intensifications of tropical cyclones can still, as they did with Patricia, surprise forecasters. It is exceptionally rare, however, for any such surprises to contaminate forecasts of mid-latitude weather systems.
