Tropical Storm Sonia Hits Mexico; Eastern Pacific Hurricane Season Likely Over

In the Eastern Pacific, Tropical Storm Sonia, the eighteenth named storm of the 2013 Eastern Pacific hurricane season, made landfall near midnight EST on Sunday near El Dorado, Mexico, as a minimal tropical storm with 40 mph winds. Heavy rains of 3 - 6 inches are expected in Mainland Mexico along the path of Sonia on Monday, potentially triggering flash floods and mudslides. Moisture from Sonia is being drawn to the northeast, where it will contribute to rains over the Central U.S. later in the week. There are currently no threat areas to discuss in the Eastern Pacific, and the GFS and European models are not predicting development of anything over the coming seven days. The last named storm of the Eastern Pacific hurricane season typically forms on November 5, so there is a good chance that Sonia will be the last storm of the year. There were no November Eastern Pacific named storms in 2012, but 2011 featured the 2nd strongest storm of the entire Eastern Pacific hurricane season in November, Category 4 Hurricane Kenneth (145 mph winds.)


Figure 1. MODIS satellite image of Tropical Storm Sonia, taken at 18:10 UTC on November 3, 2013. At the time, Sonia had top winds of about 45 mph. Image credit: NASA.

The 2013 Eastern Pacific hurricane season in perspective
Sonia's formation brings the 2013 Eastern Pacific hurricane season numbers to 18 named storms, 7 hurricanes, and 1 major hurricane. The 1981 - 2010 averages for the Eastern Pacific hurricane season are 15 named storms, 8 hurricanes, and 4 major hurricanes. Due to the lack of major hurricanes, the Accumulated Cyclone Energy (ACE) has been just 51% of average so far in 2013. NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 23, was not far from the mark. It called for a below-average season, with 11 - 16 named storms, 5 - 8 hurricanes, 1 - 4 major hurricanes, and an ACE index 60% - 105% of the median. The mid-point of these ranges gives us a forecast for 13.5 named storms, 6.5 hurricanes, and 2.5 major hurricanes, with an ACE index 82% of average.

While the raw numbers show a quiet Eastern Pacific hurricane season, one bad storm--Hurricane Manuel--made the 2013 season one of the worst in Mexico's history. Manuel made landfall on September 15 near Manzanillo as a tropical storm with 70 mph winds, and brought devastating flooding to the coast near Acapulco. Manuel was the most expensive Eastern Pacific tropical cyclone in history, with damage estimated at $4.2 billion. The 169 people it killed made it the 7th deadliest Eastern Pacific tropical cyclone on record. Only three Eastern Pacific hurricanes have had their names retired--Hurricane Ismael of 1995, Hurricane Pauline of 1997, and Hurricane Kenna of 2002. Manuel is likely to become the fourth retired name on the list.

More trouble in the Western Pacific
Tropical cyclone activity in the Western Pacific over the past month has been very high, with seven typhoons in the month of October alone. According to records at the Joint Typhoon Warning Center (JTWC), this would appear to be a new record for the number of typhoons in any October, breaking the previous record of six typhoons during October 1989 (thanks go to typhoon expert Mark Lander for this stat.) The latest system of concern is Tropical Storm Haiyan, which is gathering strength over the warm tropical waters east of the Philippines. Haiyan's formation brings the tally of named storms in the Western Pacific in 2013 to 28, making it the busiest season in that ocean basin since the 32 named storms of 2004. Satellite loops show that Haiyan is a large tropical storm with plenty of intense thunderstorms that are steadily growing more organized. Haiyan is expected to take advantage of warm waters and low wind shear and intensify into a major Category 4 typhoon by Thursday. Both the GFS and European models predict that Haiyan will pass through the central Philippines near 6 UTC on Friday. If this prediction holds true, Haiyan could be the most dangerous tropical cyclone to affect the Philippines this year--particularly since Tropical Depression Thirty is dumping heavy rains of up to one inch per hour over the central Philippines today, which will saturate the soil and make extreme flooding more likely late this week when Haiyan arrives.

Quiet in the Atlantic
An area of low pressure over the Central Caribbean is bringing disorganized heavy rain showers to the region. Wind shear is a high 20 - 30 knots, and none of the reliable models for tropical cyclone formation is predicting development during the coming five days. In their 8 am EST Tropical Weather Outlook, NHC gave the disturbance 5-day formation odds of 10%.

Jeff Masters