16:37 Sun May 29, 2016
Never Out of the Woods
Despite Tropical Storm Bonnie being the hot-button topic of most New England meteorologists' concern this weekend, it can be said with fairly high confidence that the brunt of the storm will pass well south of us here in the White Mountains. Even the northernmost tracks forecast by the EPS and GEFS (ensemble models that run dozens of slight perturbations on the one initialized model, creating a series of outputs covering the whole spectrum of what could happen) keep the system roughly 100 miles offshore. In fact, mean sea level pressure is forecast to remain well above 1000 millibars (which roughly equates to 800 mb at the summit of Mount Washington) through much of New England. Large portions of the Carolinas and Virginia are forecast to get upwards of 3 inches of rain, though the heaviest rainfall is expected to stay offshore (in excess of 8 inches).
But what would happen if Bonnie plowed through the White Mountains? Moreover, what would happen if instead of Tropical Storm Bonnie it was Hurricane Bonnie that had Mount Washington in her crosshairs? Well, that is exactly what happened on August 31, 1954, except instead of Bonnie, it was Hurricane Carol that was the culprit. Southern New England saw sustained winds in excess of 100 mph and the Observatory gusted up to 142. More noteworthy though was the tropical rainfall Mount Washington saw; over 3 inches of it. The infamous New England hurricane known only as “38” (common practice before 1954, when hurricanes were not named as they are today; they were most commonly named after the area they most affected) ravaged New England and dumped 5.45 inches of rain over the White Mountains to go along with 120 mph sustained winds and gusts of up to 160 mph. The observer comment from September 22, 1938 reads in part: “Violent winds continued with lessening force throughout the night. Many trees blown down on all sides of mountains. Road closed by fallen trees.” If such an event were to occur today, a lot more life and property would be placed in harm's way. As you can probably imagine, all the rain that falls on the White Mountains would run downslope and accumulate in the valleys thus causing major flash flooding. At 1,173 square miles, the amount of water that falls on the entirety of White Mountain National Forest during a 1 inch rain event is 20 billion gallons. So another 5.45 inch event would yield a total of over 111 billion gallons of water (enough to fill the Empire State Building over 4 times) being dumped over the area in a short period of time.
Needless to say, another storm like 38 would be a major natural catastrophe. Like with a major ice storm, the landscape can be permanently altered in the wake of these once in a lifetime events (38 was estimated to be a 100-150 year event, meaning every year there is between 0.01% and 0.067% chance of it occurring). It is safe to say the cost in dollars would far exceed the 1938 New England Hurricane, but it is also reasonable to believe that the cost in lives would be greatly reduced because of the advent of modern forecasting and technology. So even though Bonnie won't affect us, 38 serves as a grave reminder for us at the Observatory and forecasters across New England to stay vigilant because statistically speaking, there will be another 38.
Forecast rainfall associated with Tropical Storm Bonnie
Original B-16 Observer log from September 21, 1938 when "38" affected the area
Tim Greene, Summit Intern