National Environmental and Meteorological Association, Inc.

Annual Atlantic Tropical Outlook For The 2007 Season
issued Friday June 1, 2007

The following is an outlook for the 2007 Atlantic Hurricane Season. This outlook reflects the opinions of those on this Forecast Team only and is not connected to any other organization or agency. All standard NEMAS disclaimers apply, see below.

Prepared By:

Introduction

In the past decade or so, the scientific community and the public have shown considerable interest in seasonal forecasts for tropical cyclones. Such information allows the public to obtain a general idea of the expected number of cyclones during the course of June through November. It is particularly difficult to pinpoint regions which will be heavily targeted for landfalling cyclones, but recent research has made it possible to estimate a rough number of tropical storms and hurricanes that may develop.

A weak to moderate El Nino was in its developmental stages during much of the 2006 Atlantic Hurricane Season. The warm phase of the El Nino Southern Oscillation (ENSO) tends to limit overall activity in the Atlantic Basin. Even so, 10 tropical cyclones formed last year; including 9 named storms and 1 unnamed tropical storm. Of these, 5 became hurricanes; 2 were major hurricanes (category 3 or greater on the Saffir-Simpson Scale). In an average season, 10 tropical cyclones develop; 6 of which become hurricanes. 2 of these hurricanes, on average, achieve a minimum of category 3 intensity. As a result of these numbers, 2006 turned out to be an average tropical season.

All indications suggest that the 2007 Atlantic Hurricane Season will exhibit above average activity. In fact, there are early signals that hint at significantly above average activity. Below is the NEMAS Seasonal Forecast and the reasoning behind our forecast. It is important to remember that it only takes one major hurricane to cause catastrophic damage to coastal areas.

2007 Atlantic Basin Forecast

NEMAS is forecasting a total of 18 named storms in 2007. Of these 18 storms, we expect 10 to attain hurricane intensity (64 knots/74 mph or greater). And, of the 10 hurricanes, we expect 5 to become major hurricanes (96 knots/111 mph or greater).

* This is the average cumulative number of systems per year for the period 1944-2002 (data courtesy the National Hurricane Center)

** While only 9 storms were actually named in 2006, the unnamed storm did attain Tropical Storm status, which would normally be considered a named storm. So for all intents and purposes, we are going to say that there were 10 "named" storms for the 2006 season.

2007 Atlantic Basin Forecast Graphics

Click the images to enlarge

Forecast Reasoning

Recent Pattern
A very dominant large-scale pattern has been in place from March through mid-May. A deep-layer high pressure dominated areas from the Great Lakes and Northeast U.S. Southward into Dixie. Meanwhile, troughiness was observed in the western Atlantic Ocean and over the Rockies and High Plains. Such a pattern is not atypical for a developing cold phase in the Eastern Pacific Ocean. It results in drier-than-normal conditions over the eastern and southeastern United States. Research has shown that, especially in La Nina years, activity increases over the Carolinas and Virginia, northward. Therefore, higher-than-average landfall risk is forecast for North Carolina. We have included a moderate landfall risk for New England also, just in case a system along the Carolinas tracks north-northeastward and scrapes that area. Should the above-mentioned pattern, then several tropical cyclones would also recurve into the open waters of the Atlantic, too.

As of late May, a shift in the global pattern has occurred. While the influence of the North Atlantic Oscillation (NAO) tends to dampen in the warm season, a noticeable shift toward a negative anomaly has shifted the trough eastward into the Plains, while pushing the ridge into the Atlantic waters just off the eastern seaboard. The ensemble forecasts generally maintain a negative NAO pattern into the first half of June, which may allow a few systems in the Caribbean or Gulf to impact Gulf coastal areas of Florida. Here, a moderate risk of landfall is forecast for the season. However, it is our belief that the pattern change occurring in late May to early June is temporary, and that the dominate spring weather pattern will return in the summer. So in addition to the Carolinas, we will have to monitor Caribbean systems that will undercut the troughiness anticipated in the western Atlantic. This would favor an increased threat of landfalls along the vulnerable and economically-sensitive central to western Gulf coastal regions, where a high risk of landfall is indicated during the height of the hurricane season.

As always, only temporary pattern shifts at any time of the season can result in any coastal location receiving a significant hurricane hit. All residents living within 50 miles of the Gulf and Atlantic coasts should have 3-days of supplies (should they opt to ride out a hurricane), or have a plan of escape (should emergency management officials urge residents to evacuate).

El Nino/La Nina
Currently ESNO conditions in the tropical Pacific reflect neutral conditions, another words, neither El Nino or La Nina. However, the trend is toward cooling sub-surface sea temperatures which is leading toward the development of La Nina conditions. Last season at this time the opposite was occuring with warming sea temperatures leading to El Nino conditions. This is believed to be the reason that the 2006 Atlantic tropical season was rather lack-luster in terms of good quality storms. This season is likely to be quite different with at least weak La Nina conditions occuring during the Aug-Oct time period, the general peak of the hurricane season. Numerical models are predicting the development of La Nina conditions heading into the summer months, however they differ on just how cool the sea-surface temperature become over the next 3-6 months. La Nina generally favors above average tropical cyclone activity in the Atlantic Basin.

Atlantic Sea-Surface Temperatures
As of mid-May 2007, a large portion of the Atlantic Ocean south of 40 degrees North Latitude is experiencing above average water temperatures. The largest positive anomalies stretch across the central Atlantic from the Azores to just northeast of the Leeward Islands. While the western Atlantic, Gulf of Mexico, and Caribbean Sea are lagging a bit, it is expected that temperatures here will rebound rapidly over the coming weeks. As a matter of fact there are already signs of this occurring in recent weeks. The highest anomalies are currently as much as 2 to 2.5 degrees celsius above climatological values in a large area between the Azores and Leeward Islands. Near average SST's were observed northeast of the Bahamas to just southwest of Bermuda as well as across the eastern Caribbean. An area of negative anomalies is located in the western Atlantic from the U.S. East Coast eastward to about several hundred miles east and northeast of Bermuda. However, these anomalies did not exceed 1.5 to 2 degrees below climatological values. The overall trend across the Atlantic basin however is for warming ocean temperatures.

Conclusion

Based on the aforementioned meteorological and climatological factors, we are expressing strong confidence in our forecast of above average to much above average tropical cyclone activity between June 2007 and November 2007. It is extremely important that the public recognizes that an increased number of storms does not necessarily guarantee that any of these tropical cyclones will make landfall along coastal areas this season. In 2005, the Atlantic Basin produced 28 named storms, which was a record season, and brought several landfalls to the U.S., including Katrina along the central Gulf Coast. However in 1995, the Atlantic Basin produced 21 named tropical cyclones; most of which turned harmlessly out to sea. In 1992, Hurricane Andrew - the costliest hurricane in United States history - was the only landfalling hurricane in an otherwise quiet season. However, an increased number of storms will inherently increase the opportunities of a landfall somewhere in the Atlantic Basin. Residents within 50 miles of the coast between Texas and Maine (and especially Florida and North Carolina) should have a plan of action prepared before each season in case a hurricane threatens.

Disclaimer

All NEMAS Weather Forecasts are in no way generated by, supported by, or connected to NOAA, the National Weather Service, or any other organization/agency. Our forecasts are produced based on our own analysis of the situation at hand.

NEMAS is not responsible for any losses or damages, whether to life or property. We do not, and simply cannot guarantee that our forecasts will be, or are accurate 100% of the time. Please refer to the National Weather Service for official weather information.

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