Atlantic November Hurricane Outlook
3:01 PM GMT on November 01, 2013
The tropical Atlantic is quiet, with no threat areas to discuss, and no reliable models predicting development of a tropical cyclone during the coming five days. So, are we all done for 2013? Or will this unusually quiet hurricane season spawn a Tropical Storm Melissa? The large-scale circulation pattern over the first half of November favors upward-moving air and an increased chance of tropical storm development over the Atlantic, due to the current positioning of the Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days. By mid-November, this pattern will favor sinking air over the tropical Atlantic, making a late-November tropical storm an unlikely proposition. Wind shear has risen to high levels prohibitive for tropical storm formation over the Gulf of Mexico and the waters near the Bahama Islands, and is expected to remain very high through mid-November, according to the latest run of the GFS model. However, wind shear over the Caribbean is likely to be average to below average for the next two weeks, making tropical storm formation possible there. The oceans are certainly warm enough to support development, with Sea Surface Temperatures (SSTs) in the Caribbean 0.2°C (0.37°F) above average, and well above the 26°C (79°F) threshold typically needed to support tropical storm formation (Figure 1.) Dry air--which has dominated the tropical Atlantic during the 2013 hurricane season--will continue to make its presence felt over the Caribbean during portions of the coming two weeks, though, reducing the odds of development. The African Monsoon is quiet this time of year, and we no longer have African waves coming off the coast of Africa that can act as the seeds for formation of a tropical storm in the Caribbean. If we do get a tropical storm, it will probably be in the Western Caribbean, where the tail end of a cold front lingers long enough over warm waters to generate some heavy thunderstorms and acquire a spin. A cold front capable of triggering such a disturbance will arrive over the Western Caribbean November 8 - 9, but the GFS and ECMWF models are not suggesting any development from this front. Taking all these factors into account, I predict that the Atlantic hurricane season of 2013 is over, with just a 20% chance of another named storm this season.
Figure 1. Sea surface temperatures in the Atlantic on November 1, 2013. The black line marks the 26°C (79°F) isotherm, which is the boundary where tropical storm formation can typically occur. A large portion of the Atlantic is still capable of supporting tropical storm formation, but the Gulf of Mexico is getting marginal.
Climatology of November Atlantic tropical cyclones
Since the active hurricane period we are in began in 1995, eleven of the eighteen years (61%) have seen one or more Atlantic named storms form after November 1, for a total of sixteen November/December storms:
2011: Tropical Storm Sean on November 8
2009: Hurricane Ida on November 4
2008: Hurricane Paloma on November 6
2007: Tropical Storm Olga on December 11
2005: the "Greek" storms Gamma, Delta, Epsilon, and Zeta
2004: Tropical Storm Otto on November 29
2003: Odette and Peter in December
2001: Hurricane Noel on November 5 and Hurricane Olga on November 24
1999: Hurricane Lenny on November 14
1998: Hurricane Nicole on November 24
1996: Hurricane Marco on November 19
Only three of these storms (19%) caused loss of life: Hurricane Ida of 2009, which killed one boater on the Mississippi River; Tropical Storm Odette of 2007, whose floods killed eight people in the Dominican Republic; and Hurricane Lenny of 1999, which killed fifteen people in the Lesser Antilles. "Wrong-way Lenny" was both the deadliest and the strongest November hurricane on record (Category 4, 155 mph winds). There have been only seven major Category 3 or stronger hurricanes in the Atlantic after November 1. Part of the reason for the relatively low loss of life for November storms is that they tend to form from extratropical low pressure systems that get cut off from the jet stream and linger over the warm waters of the subtropical Atlantic. These type of systems typically get their start in the middle Atlantic, far from land, and end up recurving northeastwards out to sea. The most recent November named storm, Tropical Storm Sean of 2011, was an example of this type of storm. However, as I noted in the wake of Hurricane Tomas of November 2010 in my blog post, Deadly late-season Atlantic hurricanes growing more frequent, "It used to be that late-season hurricanes were a relative rarity--in the 140-year period from 1851 - 1990, only 30 hurricanes existed in the Atlantic on or after November 1, an average of one late-season hurricane every five years. Only four major Category 3 or stronger late-season hurricanes occurred in those 140 years, and only three Caribbean hurricanes. But in the past twenty years, late-season hurricanes have become 3.5 times more frequent--there have been fifteen late-season hurricanes, and five of those occurred in the Caribbean. Three of these were major hurricanes, and were the three strongest late-season hurricanes on record". Dr. Jim Kossin of the University of Wisconsin published a 2008 paper in Geophysical Research Letters titled, "Is the North Atlantic hurricane season getting longer?" He concluded that yes, there is an "apparent tendency toward more common early- and late-season storms that correlates with warming Sea Surface Temperature but the uncertainty in these relationships is high". The recent increase in powerful and deadly November hurricanes would seem to support this conclusion.
Figure 2. The strongest hurricane on record in the Atlantic in November, Hurricane Lenny, takes aim at the Lesser Antilles on November 17, 1999. Image credit: NOAA.