Tuesday, July 9, 2013

2013 Hurricane Season: Very Active?

It has been a little over a month since the last of the 2013 hurricane season forecasts were made.  All of the forecasts call for an active season with the possibility of a very active season.  The third named storm of the season (Chantal) formed late on July 6, which is just over a month earlier than when the average “C” storm forms.  Is this a sign of a very active season?  Given conditions in the tropics I would say, yes.

Tropical Storm Chantal moves into the eastern Caribbean Sea.  Click on image for a larger view.  Credit: NOAA.

Two storms have already formed in the deep tropics (Barry, Chantal) and one is a Cape Verde storm which usually doesn’t get going until mid-August.  As Jeff Masters points out on his blog:

"Most years do not have named storm formations in June and July in the tropical Atlantic (south of 23.5°N); however, if tropical formations do occur, it indicates that a very active hurricane season is likely. For example, the seven years with the most named storm days in the deep tropics in June and July (since 1949) are 1966, 1969, 1995, 1996, 1998, 2005, and 2008. All seven of these seasons were very active. When storms form in the deep tropics in the early part of the hurricane season, it indicates that conditions are already very favorable for TC development. In general, the start of the hurricane season is restricted by thermodynamics (warm SSTs, unstable lapse rates), and therefore deep tropical activity early in the hurricane season implies that the thermodynamics are already quite favorable for tropical cyclone (TC) development."

This quote is attributed to Colorado State University researchers Phil Klotzbach and Bill Gray.

There is no question that the tropical North Atlantic waters are warm.  They are above normal from the coast of Africa to the Gulf of Mexico.  The map below shows the sea-surface temperature anomaly for the North Atlantic basin as of early July.  Note that water temperatures are still above normal off the northeast coast of the U.S.

Sea-surface temperature anomaly for the North Atlantic on July 6, 2013.  Click on image for a larger view.  Image Credit: NCEP/NWS/NOAA.
Keep in mind that the El Nino – Southern Oscillation (ENSO) is in a neutral phase and that no El Nino or La Nina influence is expected during this hurricane season.  There may be short-term influences from weather patterns, but these cannot be forecast much beyond two weeks.

Also, we have been experiencing a heightened level of tropical activity since 1995.  This phase is likely to continue for at least another decade.

Image Credit: Climate Central.

Here is a summary of all of the groups making hurricane seasonal forecasts:

Click on image for a larger view.  Image Credit: FSU/COAPS.

The bottom line is be prepared.  It may be a long hurricane season.  Weather patterns favor storms moving into the Gulf or up the East coast.  The Bermuda high has been quite close to the U.S. at times this season.  This could help steer storms into the U.S.

The last three seasons have been tied for the third busiest seasons on record with 19 named storms in each year.  I see no reason to think it will be different this year.