Otto Shifts from Atlantic to Pacific after Historic Landfall in Central America

Tropical Storm Otto is now in the Eastern Pacific, headed westwards away from Central America, after making landfall on Thursday as a top-end Category 2 storm with 110-mph winds over southern Nicaragua. Otto’s heavy rains are being blamed for four deaths on November 22 in Panama, and at least five others are missing there. These deaths are the second latest deaths on record from an Atlantic named storm that we are aware of; the only killer storm on record later in the year was Tropical Storm Odette, whose floods killed eight people in the Dominican Republic after making landfall on December 6, 2003. Damage from Otto may be relatively light for its strength given that the hurricane made landfall in a very sparsely populated part of far southern Nicaragua.

Otto’s circulation survived its trek over Central America remarkably well, as the center emerged from the west coast of Costa Rica as a 70-mph tropical storm. In records dating back to 1851, Otto is the only tropical storm or hurricane whose center moved over any part of Costa Rica. Otto is also the Atlantic’s latest hurricane landfall in any year, and the latest Atlantic hurricane to reach Category 2 strength in any year.


Figure 1. MODIS satellite image of Otto taken at approximately 11 am EST, November 24, 2016--Thanksgiving Day. At the time, Otto was a Category 2 storm with 110 mph winds about to make landfall in Nicaragua as the strongest Atlantic hurricane ever observed so late in the year. Image credit: NASA.


Figure 2. Civil Defense workers look at the area where a couple was killed after their home was destroyed by a mudslide in Arraijan on the outskirts of Panama City, Panama on Nov. 22, 2016. Image credit: AP Photo/Arnulfo Franco.

According to insurance broker Aon Benfield, at least four people were killed in Panama, including two who were trapped in a landslide that struck just west of Panama City. Seven people were rescued from the slide. The third fatality was reported as the result of a toppled tree in Panama City while the fourth was as the result of drowning in the swollen Utivé River. Five people were officially listed as missing.

Otto’s future
As of 10 AM EST Friday, Otto was located more than 150 miles west of Costa Rica, with top sustained winds still at 65 mph. Few tropical storms traverse the East Pacific this far southeast, and computer models have been struggling to capture Otto’s initial state and come into agreement on its future. The rough consensus is for a steady-state tropical storm over the next several days, with some weakening thereafter. Otto will be moving over warm water with sea surface temperatures of 28 - 29°C (82 - 84°F, or about 1 - 2°C above average) with moderate wind shear of 15 - 20 knots and a reasonably moist atmosphere (mid-level relative humidity around 60%). The 06Z Friday run of our most reliable intensity model, the HWRF, projects a gradual weakening, with Otto close to the bottom threshold of tropical storm strength by next Wednesday. Meanwhile, statistical models, including the 12Z SHIPS run, suggest that Otto could actually gain some strength by early next week. The 10 AM EST Friday outlook from the National Hurricane Center (NHC) predicts that Otto will weaken to a post-tropical remnant low between Tuesday and Wednesday.

From Atlantic to Pacific: a first in hurricane naming
Tropical Storm Otto is the first storm on record to carry the same name while moving from the North Atlantic to the Northeast Pacific or vice versa. In all such prior events, NHC policy was to assign a different name when an identifiable tropical cyclone moved from one basin to another. NHC’s subsequent name-retention policy was adopted more than a decade ago, but Otto is the first storm to put the rule into practice. Under the old rule, five tropical storms or hurricanes--including the most recent, Hurricane Cesar-Douglas (1996)--underwent a name change when moving from Atlantic to Pacific or vice versa. A few other “crossover” tropical cyclones have been recorded, most of them moving from Atlantic to Pacific rather than vice versa. Some of these were no more than a tropical depression in one or the other basin, which meant that only one name was used during the entire life cycle. The most recent of these was Hermine (2010), which formed as an East Pacific tropical depression before entering the western Gulf and striking the northeast coast of Mexico as a tropical storm.

As part of the new naming convention, Otto in the East Pacific has been assigned a different ID than Otto in the Atlantic under the U.S. Automated Tropical Cyclone Forecasting System (ATCF), even though the storm has the same name and is considered the same cyclone in both basins. This is playing havoc with various online platforms that map and archive tropical cyclones. At the National Hurricane Center’s website, and on our own site, you’ll see a Hurricane Otto in the Atlantic and a Tropical Storm Otto in the Pacific depicted as two separate tropical cyclones. It appears that the two life stages of Otto will be considered separately when calculating storm totals and Accumulated Cyclone Energy for the 2016 Atlantic and East Pacific seasons.

Hurricane landfalls from January to November?!
Between the landfall of Hurricane Alex in the Azores in January and Otto's landfall in Central America this week, 2016 will break the record for the most prolonged calendar-year hurricane season in Atlantic history (the 1938 season is close behind, although that one wasn’t bracketed by landfalls). "WX Geeks" host Marshall Shepherd reflects on this "year-long" hurricane season in a Forbes essay published Friday.

We’ll be back with our next post on Monday. Enjoy the weekend, everyone!

Jeff Masters and Bob Henson