Over the past few days you might have viewed my briefings on Hurricane Sandy. From a meteorological and impact perspective, this will be a historic event.
I have heard a lot of post-event discussion on the causes for such a major event. I’d like to add some perspective to this discussion.
There is always a rush to speculate on the meteorological understanding on major weather disasters. I am sure that there will be plenty of research on Sandy, for years to come. I would like to briefly discuss aspects of this event that I feel were unusual, or not.
Time of Season: While it is very late in the season, tropical storms and hurricanes can, and do, form in late September and even November. There was a lingering pool of warmer water in the region where Sandy formed that likely led to the formation. Tropical Storms and hurricanes are also not as likely to move inland over the Northeast U.S. as other coastal areas, but there is climatology of such storms impacting the region. Thus, unusual but not unprecedented.
Size of the Storm: Sandy was a huge system. I’m not sure where it stands in term of size compared to a record event, but again, I’d classify this as unusual but likely not unprecedented.
Atmospheric Pressure: Sandy produced a near-record low barometric pressure of 27.76 inches. This was the second lowest pressure north of Cape Hattaras (lowest was Hurricane Gladys in 1977). However, this low pressure, especially with a Category I hurricane is highly unusual.
Storm Surge: I’m sure that there will be plenty of study and research into storm surge as it produced the greatest impacts. I suspect that the reason that the surge was so high was the unfortunately linkage with a number of other factors, including wave action, storm surge, enhanced surge due to “ideal” on-shore forcing, phase of the moon, and high tide. The “regular” surge with Sandy most likely would have been typical for the intensity of storm, however when aligned with all of these other factors, the surge was significantly enhanced. Thus, the alignment of all of these enhancing factors was quite unusual.
Rainfall: Not unusual. The highest accumulation I have seen so far was around 15”. This is not at all uncommon for any inland-moving tropical system.
Inland Flooding: Not unusual. Inland rainfall amounts were typical, or even below normal, for a tropical system. Consequently, inland flooding on main stem rivers was limited. Widespread pooling of water and urban flooding (inland) was typical for such an event.
Snowfall: The set up for the record snowfall, including tropical moisture feeding into the colder air and higher elevation,s is indeed unusual. While I suspect it might not be unprecedented. it was highly usual.
Entire event: While each individual aspect of Sandy might not be a record or highly unusual, the scope of the entire event is one for the record books and likely is unprecedented, at least throughout recent history.
Southwest and South U.S. – Continue Trend Alert for Dry Weather
I am continuing my long-standing trend for dry weather over the Southwest U.S. and portions of Texas. This region has received very little rainfall for weeks and it looks like no significant rainfall can be expected for at least the next 10 days.
Southeast U.S. – Continue Trend Alert for Dry Weather
The Southeast U.S. also looks quite dry. While there will be some weak frontal passages that will bring light precipitation from time to time, below-normal precipitation will continue through the first week of November.
Pacific Northwest – Trend Alert for Wet Weather Discontinued After Saturday
Pacific Northwest – the long-standing inflow of moisture will continue this week but I expect it to break with drier conditions next week.