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Ariel E. Cohen and John P. Cangialosi

Abstract

The Tropical Analysis and Forecast Branch (TAFB) of the National Oceanic and Atmospheric Administration’s (NOAA’s) National Hurricane Center in Miami, Florida, provides high-seas forecasts to portions of the eastern Pacific Ocean, including the Gulf of California. These forecasts include wind velocity and significant wave height forecasts and are initiated by forecast winds of at least 20 kt (10.3 m s−1) or significant wave heights of at least 8 ft (2.4 m). The Gulf of California is a commonly traveled area, where winds are highly modulated by nearby terrain variations. This provides a unique forecast challenge, especially in the absence of regular surface observations. In October and November 2008, the NOAA R/V David Starr Jordan was stationed in the Gulf of California and occasionally reported gale force winds [34–47 kt (17.5–24.2 m s−1)], which operational models regularly missed. A ship log of these events provided the basis for determining mean and anomaly fields for a handful of meteorological variables, from which a conceptual model for the synoptic-scale environment supporting these events is presented. An index based on the mean sea level pressure (MSLP) difference between Ely, Nevada, and Yuma, Arizona, was developed to measure the potential for gales, which was found to be statistically significant in discriminating between “gale” and “marginal wind” events. The fifth-generation NCAR–Pennsylvania State University Mesoscale Model (MM5) is used to conduct doubly nested high-resolution simulations centered on the Gulf of California. These simulations appeared to resolve the gales better than traditional global model guidance, lending credence toward the need for high-resolution modeling in areas of highly variable terrain. Relatively small errors were found in MM5 output using the National Aeronautics and Space Administration (NASA) Quick Scatterometer (QuikSCAT) data as verification.

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Christopher W. Landsea and John P. Cangialosi

Abstract

The tropical cyclone is the largest single-day-impact meteorological event in the United States and worldwide through its effects from storm surge, extreme winds, freshwater flooding, and embedded tornadoes. Fortunately, over the last three decades there have been incredible advances in forecast accuracy, especially for the track of the tropical cyclone’s center. Errors have been cut by two-thirds in just 25 years due to global modeling advances, data assimilation improvements, dramatic increases in observations primarily derived from satellite platforms, and use of ensemble forecast techniques. These four factors have allowed for highly accurate synoptic-scale atmospheric initial conditions and forecasts of the steering flow out through several days into the future. However, such improvements cannot continue indefinitely. It is well known in the atmospheric sciences that there exists an inherent “limit of predictability” because of errors at the smallest scales (microscale—meters and seconds) that eventually cascade up to the largest scales (synoptic scale—thousands of kilometers and several days). While there have been estimates of the limits of predictability for tropical cyclone track prediction in the past, our current capabilities have exceeded those somewhat pessimistic earlier outlooks. This essay discusses the current state of the art for tropical cyclone track prediction and reassesses whether reaching the “limit of predictability” is imminent. The ramifications of this eventual conclusion—whether in the short-term or still decades away—could be critical for all users of tropical cyclone track forecast information, including the emergency management community/governments, the media, the private sector, and the general public.

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Stacy R. Stewart and John P. Cangialosi

Abstract

The 2010 eastern North Pacific hurricane season was one of the least active seasons on record. Only seven named storms developed, which is the lowest number observed at least since routine satellite coverage of that basin began in 1966. Furthermore, only three of those storms reached hurricane status, which is also the lowest number of hurricanes ever observed in the satellite-era season. However, two tropical storms made landfall: Agatha in Guatemala and Georgette in Mexico, with Agatha directly causing 190 deaths and moderate to severe property damage as a result of rain-induced floods and mud slides. On average, the National Hurricane Center track forecasts in the eastern North Pacific for 2010 were quite skillful.

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John P. Cangialosi and Christopher W. Landsea

Abstract

While the National Hurricane Center (NHC) has been issuing analyses and forecasts of tropical cyclone wind radii for several years, little documentation has been provided about the errors in these forecasts. A key hurdle in providing routine verification of these forecasts is that the uncertainty in the wind radii best tracks is quite large for tropical cyclones that are well away from land and unmonitored by aircraft reconnaissance. This study evaluates the errors of a subset of NHC and model 34-, 50-, and 64-kt (1 kt = 0.514 m s−1) wind radii forecasts from 2008 through 2012 that had aircraft reconnaissance available at both the initial and verification times. The results show that the NHC wind radii average errors increased with forecast time but were skillful when compared against climatology and persistence. The dynamical models, however, were not skillful and had errors that were much larger than the NHC forecasts, with substantial negative (too small) biases even after accounting for their initial size differences versus the tropical cyclone’s current wind radii. Improvements in wind radii forecasting will come about through a combination of better methods for observing tropical cyclone size as well as enhanced prediction techniques (dynamical models, statistical methods, and consensus approaches).

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John P. Cangialosi, Todd B. Kimberlain, John L. Beven II, and Mark Demaria

Abstract

The Dvorak technique is used operationally worldwide for tropical cyclone intensity analysis. This study tests Dvorak intensity change constraints, using a database of simultaneous aircraft and satellite fixes for tropical cyclones (TCs) in the 1998–2012 period. Results indicate that, in the vast majority of cases, Dvorak intensity constraints are valid with only a small percentage of strengthening TCs violating the constraints. Of the small sample that broke the constraints, most had initial intensities ranging from moderately strong tropical storms to minimal hurricanes.

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John P. Cangialosi, Eric Blake, Mark DeMaria, Andrew Penny, Andrew Latto, Edward Rappaport, and Vijay Tallapragada

Abstract

It has been well documented that the National Hurricane Center (NHC) has made significant improvements in Atlantic basin tropical cyclone (TC) track forecasting during the past half century. In contrast, NHC’s TC intensity forecast errors changed little from the 1970s to the early 2000s. Recently, however, there has been a notable decrease in TC intensity forecast error and an increase in intensity forecast skill. This study documents these trends and discusses the advancements in TC intensity guidance that have led to the improvements in NHC’s intensity forecasts in the Atlantic basin. We conclude with a brief projection of future capabilities.

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