El Niño Could Bring Early End to Atlantic Hurricane Season
A weather.com analysis of NOAA's best-track dataset from 1950-2014 finds that Atlantic hurricane seasons during a strong El Niño see the last named storm end two to three weeks earlier – a mean date of Oct. 18 – than the long-term average date of Nov. 5.
A strong El Niño hurricane season was defined as one during which a three-month running mean sea-surface temperature (SST) anomaly of 1.5 degrees Celsius or greater was measured at some point in the strip of ocean used to define El Niño and its counterpart, La Niña.
In both 1993 and 1960, the season's last named storm fizzled in late September. The same was true in the 1983 season, when the strong 1982-1983 El Niño fizzled after early summer, but still only spawned four named storms that season. (Though, one of those was the highly-destructive Alicia in the Houston metro area). With wind shear – the difference in wind speed and/or direction with height – typically rising from mid-September on, it only stands to reason that this hostile ingredient will only become more of a tropical cyclone squelcher in the weeks ahead.
"El Niño normally peaks in late November and December, so, on average, it has a greater effect on the second half of the hurricane season," says senior hurricane specialist Bryan Norcross (Wunderblog). But that just means that the odds of a named storm are lower. On any one day, there are many still pockets in the Atlantic Ocean or Gulf of Mexico that are favorable for tropical development."
Furthermore, while the Atlantic may struggle to maintain long-lived tropical cyclones from the deep tropics during this strong El Niño, more systems spinning up much closer to the U.S., such as we saw with Ana and Bill early in the season, could still occur into October.
The bottom line on the 2015 Atlantic hurricane season, says Norcross: "It's not over until it's over."
Average date the last named storm of the Atlantic hurricane season (that was at least tropical storm-force) was downgraded from a tropical cyclone for strong, moderate and weak El Nino seasons (since 1950). The average date (1950-2014) is also shown.
Named storm tracks in the 2015 Atlantic hurricane season through September 14.
Original Article: http://www.wunderground.com/news/el-nino-end-atlantic-hurricane-season-early-sep2015
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