Wrapups with Records...
Posted December 3, 2007
We closed out both the month of November and the 2007 Atlantic Hurricane season on Friday, with a couple of modest records to note with the ending of the month.
First, November turned out to be the driest on record for the Raleigh-Durham airport, with .48 inches of rain recorded, compared to a normal of 2.97 inches for the month historically. While this is a very low rainfall amount and is ill-timed as it contributes to worsening the ongoing drought, it isn't an unprecedented figure when you take a broad look at past readings. The same location was almost as dry in 2001 with .50 inches and not much wetter in 1973 when .61 inch was recorded. In addition, we can look back through stations that served as the official site for Raleigh prior to the airport, for which we have readings stretching back to 1887. During that period, there were two years (1890 and 1931) in which only 6 hundredths of an inch were measured in November.
Also of note is that the rain we have had this year has been concentrated into a relatively low number of days. At RDU, measurable rain (one hundredth of an inch or more) has occurred 82 times, which places us within striking distance of the RDU record for fewest in a calendar year, which is 92 days in 1953, 1965, and 1969. The average number of days with rain in a year at RDU is 113, and we average 10 of those during the month of December.
The other wrapup this week is hurricane season, and barring an out-of-season storm or two in the next few weeks we'll close out the 2007 season with 14 named storms and six hurricanes for an above normal season in terms of named storms but a near-normal year for hurricanes. In addition to tracking those numbers, one can integrate the duration and intensity figures for all the storms using an index such as the NOAA's Accumulated Cyclone Energy index or the Power Dissipation Index used by some other researchers. By this measurement, the season fell short of the long-term median, due to a sizable number of relatively weak and/or short-lived storms. Even so, there were two landfalling Category 5 hurricanes this season, Dean and Felix, and that has not previously occurred in the hurricane records that area currently available stretching back to 1851. For more details on the storms that did form this year, see http://www.nhc.noaa.gov/archive/2007/tws/MIATWSAT_nov.shtml, and for another overview of the past season and some speculation regarding factors that resulted in a less impressive year than expected, see http://www.noaanews.noaa.gov/stories2007/20071129_hurricaneend.html.
Just for comparison purposes, here is a snippet from my blog here of May 28, 2007, with a roundup of then-current outlooks for the upcoming season... "Taking a look at three sources of seasonal forecasts, we have NOAA projecting 13-17 named storms and 7-10 hurricanes, while Dr William Gray's group at Colorado State University expects 17 named storms and 9 hurricanes. An NCSU team led by Dr Lian Xie also expects an above normal season for 2007, calling in a recent press release for 12-14 named storms and 8-9 hurricanes.These numbers compare to long-term averages of 10 named storms and 6 hurricanes." In the end, all of the groups forecast more hurricanes than developed, but the "named storms" predictions were not too far off, especially for the NCSU group.