Hurricane experts at the National Oceanic and Atmospheric Administration (NOAA) said Monday that they expect the 2003 Atlantic hurricane season to have above normal levels of activity, which supports an earlier forecast by Dr. William Gray of Colorado State University (see Daily GPI, April 7).
NOAA’s outlook calls for the potential of 11 to 15 tropical storms, with six to nine hurricanes, and two to four classified as major hurricanes (category 3 or higher on the Saffir-Simpson Hurricane Scale). In comparison, Gray’s team of meteorologists predict that there will be eight hurricanes, three of them intense hurricanes and a total of 12 named storms this year.
Last year there were 12 named storms, but only four hurricanes (Gustav, Isidore, Kyle and Lili), and only two of those ever made it past category three intensity (winds 111-130 mph). Nevertheless, 2002 was an active year in the Gulf of Mexico with six named storms and significant disruption to natural gas and petroleum producing infrastructure, operations and supply mainly because of tropical storm Hanna and hurricanes Isidore and Lili, the last of which made it to category four intensity (winds 131-155 mph) while it was moving through offshore Louisiana production facilities.
“This year the Atlantic hurricane outlook calls for a 55% chance of an above normal season, a 35% chance of near normal, and only a 10% chance for a below-normal season such as last year,” said James R. Mahoney, deputy NOAA administrator. “In the past two years alone, nine tropical storms and one hurricane hit the United States causing 54 deaths and $6.3 billion in direct economic damage. The toll can be even higher when people are not prepared.”
On average the Atlantic hurricane season brings 10 tropical storms, with six reaching hurricane strength and two of those classified as major. Above normal activity has been observed during six of the last eight Atlantic hurricane seasons, reflecting an overall larger number of tropical storms and hurricanes observed since 1995, NOAA said.
The main factors contributing to the expected above normal Atlantic hurricane season are the existing multi-decadal patterns (lower vertical wind shear, a favorable African Easterly Jet, weaker Trade Winds, and warmer than normal Atlantic Ocean temperatures) combined with a 70% chance that La Nina conditions will develop during the summer and further reduce the vertical wind shear in the heart of the hurricane development region. La Nina is characterized by unusually cold ocean temperatures in the Equatorial Pacific, compared with El Nino’s unusually warm ocean temperatures.
“This combination of factors creates a high likelihood of an above-normal Atlantic hurricane season,” said Gerry Bell from the NOAA Climate Prediction Center. “If La Nina conditions develop as expected, then the activity could well be in the upper portion of our predicted range. This is the first time since 1999 that conditions have the potential for producing a very active season.”
Bell also noted, “On average two to three hurricanes hit the United States in seasons such as this, but we cannot say at this time whether a particular locality will be impacted by a hurricane.”
NOAA also released a drought update last week showing that above-average precipitation throughout much of the United States during the past three months led to improving drought conditions in many areas. Twenty-four percent of the contiguous United States was in moderate-to-extreme drought in April, down from 37% in January and 50% during the summer of 2002, based on a widely used measure of drought severity, the Palmer Drought Index.
Wetter-than-average conditions were prevalent in the mid-Atlantic, Southeast and in most states of the western United States. Near-average to drier-than-average conditions stretched from Maine to the Upper Midwest and southwest to Texas. The precipitation helped alleviate extremely dry conditions in many areas, but the rain and snowfall were not sufficient to end the drought in many parts of the West, where severe drought has occurred for much of the past three to five years. In Colorado, which had its driest year on record in 2002, a single snow storm in March brought a near-record snowfall of 32 inches to Denver Stapleton Airport and totals exceeding 80 inches in higher-elevation locations to the West.
Snow pack, an important source of water for western states, was near or above average at the end of April in much of the front range of the Rocky Mountains from Montana to Colorado and the Sierra Mountains, but snow pack remained below average in large parts of the West. Reservoir storage was also below average in every western state except Washington at the end of April, and river flows remained below average in a large part of the western two-thirds of the nation.
In Montana, where conditions in parts of the state during the summer of 2002 were similar to those experienced during the Dust Bowl years of the 1930s, above average precipitation during the past several months led to a marked improvement in drought conditions. However, according to the U.S. Drought Monitor, severe drought continued to affect a large part of the state at the end of April.
Based on the Palmer Drought Index, the percent of the West in moderate to extreme drought decreased from 81% in November 2002 to 44% in April. The most widespread drought in the instrumental record occurred in July of 1934, when 97% of the West and 80% of the contiguous United States were in moderate to extreme drought. The percent of the contiguous United States in moderate to extreme drought fell to 24% in April.
Temperatures during the February-April 2003 period were near average to slightly warmer than average across most of the country. The Northeast was the only region with significantly cooler-than-average temperatures. For the contiguous United States as a whole the February-April temperature was 43.3 degrees F (6.3 C), slightly warmer than the 1895-2003 mean.
The moderate El Nino episode that began in 2002 weakened during the February-April period, while the average global temperature for combined land and ocean surfaces (based on preliminary data) during April was 0.9 degrees F (0.5 C) above the 1880-2002 long-term mean. The year-to-date global average for combined land and ocean surfaces was the third warmest on record.
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