Tropical Storm Amanda Forms in the Eastern Pacific; Not a Threat to Land

The season's first named storm of 2014, Tropical Storm Amanda, has formed in the Eastern Pacific. Amanda is over 600 miles southeast of Manzanillo, Mexico, and is not a threat to any land areas. The arrival date of May 23 for season's first Eastern Pacific tropical storm is a bit early, compared to climatology. Usually, the first tropical storm of the season arrives on June 10, and the first hurricane on June 26. Last year, the season's first tropical storm, Alvin, formed on May 15, and the first hurricane, Barbara, occurred on May 29.


Figure 1. Friday morning satellite image of newly-born Tropical Storm Amanda.

Satellite loops show that Amanda has a moderately large area of heavy thunderstorms that are increasing in areal extent and intensity. WInd shear is low, 5 - 10 knots, and the SHIPS model shows that sea surface temperatures (SSTs) are a very warm 29°C, which is well above the typical 26°C threshold needed to maintain a tropical storm. All conditions appear in place to allow Amanda to intensify into a hurricane, and the official NHC forecast brings Amanda to Category 1 strength by Sunday. On Tuesday, Amanda is expected to turn to the north and encounter higher wind shear and cooler waters, which should weaken the storm.


Figure 2. The departure of sea surface temperature from average over the Eastern Pacific shows a large area of warmer than average water over the typical hurricane breeding grounds off the coast of Mexico. These warm waters will likely persist through the summer and into fall, due to a developing El Niño event, and promote a more active than usual Eastern Pacific hurricane season.

NOAA predicts an above-normal or near-normal Eastern Pacific hurricane season: 17 named storms
As is usually the case when an El Niño event is threatening, NOAA's pre-season prediction for the Eastern Pacific hurricane season, issued on May 22, is calling for an active season. NOAA expects there to be 14 - 20 named storms, 7 - 11 hurricanes, 3 - 6 major hurricanes, and an ACE index 95% - 160% of the median. The mid-point of these ranges gives us a forecast for 17 named storms, 9 hurricanes, and 4.5 major hurricanes, with an ACE index 127.5% of average. The 1981 - 2010 averages for the Eastern Pacific hurricane season are 15 named storms, 8 hurricanes, and 4 major hurricanes. The outlook calls for a 50% chance of an above-normal season, a 40% chance of a near-normal season, and a 10% chance of a below-normal season. El Niño decreases the vertical wind shear over the tropical Eastern Pacific, favoring the development of more and stronger tropical cyclones. Since 1995 the Eastern Pacific has been in an era of low activity for hurricanes, but this pattern is expected to be offset in 2014 by the impacts of El Niño.

Atlantic hurricane season begins June 1
The Atlantic hurricane season starts in just over a week, and the long-range GFS model continues to suggest that the Western Caribbean will be capable of brewing the season's first "Invest" during the first week of June. The Madden Julian Oscillation (MJO), a pattern of increased thunderstorm activity near the Equator that moves around the globe in 30 - 60 days, is currently weak, but the latest GFS forecast predicts that the MJO will strengthen slightly in early June, and might be in a position to increase thunderstorm activity over the Western Caribbean then. While long range 10 - 16 day forecasts are notoriously unreliable, early June is a common time of year for the Western Caribbean to see a tropical disturbance form. Residents of Cuba, the Cayman Islands, Jamaica, Honduras, and Nicaragua should anticipate the possibility of a multi-day period of disturbed weather with heavy rainfall beginning around June 1.

Have a great Memorial Day weekend, everyone!

Jeff Masters