Kimberly M. Wood

The influence of eastern Pacific tropical cyclone remnants on the southwestern United States

Abstract Forty-three eastern North Pacific tropical cyclone remnants with varying impact on the southwestern United States during the period 1992–2005 are investigated. Of these, 35 remnants (81%) brought precipitation to some part of the southwestern United States and the remaining 8 remnants (19%) had precipitation that was almost entirely restricted to Mexico, although cloud cover did advect over the southwestern United States in some of these cases. Although the tropical cyclone–strength winds rapidly diminish upon making landfall, these systems still carry a large quantity of tropical moisture and, upon interaction with mountainous topography, are found to drop up to 30% of the local annual precipitation. Based on common rainfall patterns and large-scale circulation features, the tropical cyclones are grouped into five categories. These include a northern recurving pattern that is more likely to bring rainfall to the southwestern United States; a southern recurving pattern that brings rainfall across...

An Updated Climatology of Tropical Cyclone Impacts on the Southwestern United States

A dataset of 167 eastern North Pacific tropical cyclones (TCs) is investigated for potential impacts in the southwestern United States over the period 1989‐2009 and evaluated in the context of a 30-yr climatology. The statistically significant patterns from empirical orthogonal function (EOF) analysis demonstrate the prevalence ofamidlatitudetroughpatternwhenTC-relatedrainfalloccursinthesouthwesternUnitedStates. Conversely, the presence of a strong subtropical ridge tends to prevent such events from occurring and limits TC-related rainfallto Mexico. These statistically significant patternscorrespondwell with previous work.The El Ni~ Oscillation phenomenon is shown to have some effect on eastern North Pacific TC impacts on the southwestern United States, as shifts in the general circulation can subsequently influence which regions receive rainfall from TCs or theirremnants. The Pacific decadaloscillation may have a greater influence during the period of study as evidenced by EOF analysis of sea surface temperature anomalies.

A 40-Year Climatology of Extratropical Transition in the Eastern North Pacific

AbstractA 42-yr study of eastern North Pacific tropical cyclones (TCs) undergoing extratropical transition (ET) is presented using the Japanese 55-yr Reanalysis dataset. By using cyclone phase space (CPS) to differentiate those TCs that undergo ET from those that do not, it is found that only 9% of eastern North Pacific TCs that developed from 1971 to 2012 complete ET, compared with 40% in the North Atlantic.Using a combination of CPS, empirical orthogonal function (EOF) analysis, and composite analysis, it is found that the evolution of ET in this basin differs from that observed in the North Atlantic and western North Pacific, possibly as a result of the rapidly decreasing sea surface temperatures north of the main genesis region. The presence of a strong, deep subtropical ridge extending westward from North America into the eastern North Pacific is a major factor inhibiting ET in this basin. Similar to other basins, eastern North Pacific ET generally occurs in conjunction with an approaching midlatitud...

A definition for rapid weakening of North Atlantic and eastern North Pacific tropical cyclones

Periods of 24 h over-water weakening during 1982–2013 for North Atlantic (NAL) and eastern North Pacific (ENP) tropical cyclones (TCs) are examined to determine a threshold for rapid weakening (RW). These periods are defined by consistent weakening while the TC center remained more than 50 km from land. Weakening thresholds of 25, 30, and 35 kt represent the 87th (69th), 94th (80th), and 97th (89th) percentile in the NAL (ENP). Based on these statistics, the 30 kt threshold is chosen to define RW. Compared to all weakening periods, RW events are generally associated with greater 24 h official forecast errors, and these errors tend to be overestimates in both basins. These events usually occur as the TC crosses a sharp sea surface temperature gradient, encounters greater vertical wind shear, and entrains drier air. These metrics may be useful to forecasters assessing the likelihood of RW.

Satellite-Derived Tropical Cyclone Intensity in the North Pacific Ocean Using the Deviation-Angle Variance Technique

AbstractThe deviation-angle variance technique (DAV-T), which was introduced in the North Atlantic basin for tropical cyclone (TC) intensity estimation, is adapted for use in the North Pacific Ocean using the “best-track center” application of the DAV. The adaptations include changes in preprocessing for different data sources [Geostationary Operational Environmental Satellite-East (GOES-E) in the Atlantic, stitched GOES-E–Geostationary Operational Environmental Satellite-West (GOES-W) in the eastern North Pacific, and the Multifunctional Transport Satellite (MTSAT) in the western North Pacific], and retraining the algorithm parameters for different basins. Over the 2007–11 period, DAV-T intensity estimation in the western North Pacific results in a root-mean-square intensity error (RMSE, as measured by the maximum sustained surface winds) of 14.3 kt (1 kt ≈ 0.51 m s−1) when compared to the Joint Typhoon Warning Center best track, utilizing all TCs to train and test the algorithm. The RMSE obtained when t...

Interannual variability of tropical cyclone activity along the Pacific coast of North America

The interannual variability of near-coastal eastern North Pacific tropical cyclones is described using a data set of cyclone tracks constructed from U.S. and Mexican oceanic and atmospheric reports for the period 1951-2006. Near-coastal cyclone counts are enumerated monthly, allowing us to distinguish interannual variability during different phases of the May-November tropical cyclone season. In these data more tropical cyclones affect the Pacific coast in May-July, the early months of the tropical cyclone season, during La Nina years, when equatorial Pacific sea surface temperatures are anomalously cool, than during El Nino years. The difference in early season cyclone counts between La Nina and El Nino years was particularlypronounced during the mid-twentieth century epoch when cool equatorial temperatures were enhanced as described by an index of the Pacific Decadal Oscillation. Composite maps from years with high and low near-coastal cyclone counts show that the atmospheric circulation anomalies associated with cool sea surface temperatures in the eastern equatorial Pacific are consistent with preferential steering of tropical cyclones northeastward toward the west coast of Mexico.

The Extratropical Transition of Tropical Cyclones. Part I: Cyclone Evolution and Direct Impacts

AbstractExtratropical transition (ET) is the process by which a tropical cyclone, upon encountering a baroclinic environment and reduced sea surface temperature at higher latitudes, transforms into an extratropical cyclone. This process is influenced by, and influences, phenomena from the tropics to the midlatitudes and from the meso- to the planetary scales to extents that vary between individual events. Motivated in part by recent high-impact and/or extensively observed events such as North Atlantic Hurricane Sandy in 2012 and western North Pacific Typhoon Sinlaku in 2008, this review details advances in understanding and predicting ET since the publication of an earlier review in 2003. Methods for diagnosing ET in reanalysis, observational, and model-forecast datasets are discussed. New climatologies for the eastern North Pacific and southwest Indian Oceans are presented alongside updates to western North Pacific and North Atlantic Ocean climatologies. Advances in understanding and, in some cases, mode...

The Unusual Behavior and Precipitation Pattern Associated with Tropical Storm Ignacio (1997)

A case study of eastern North Pacific Tropical Storm Ignacio (1997), which brought rainfall to the southwestern United States as a tropical cyclone and to the northwestern United States as an extratropical cyclone, is presented. This tropical cyclone formed from a region of disturbed weather, rather than a tropical wave, outside the typical eastern North Pacific genesis region and intensified into a tropical storm coincident with the passage of an upper-tropospheric trough. Moisture transported from Ignacio along an outflow jet associated with the trough resulted in precipitation in Mexico and the southwestern United States. As Ignacio moved north and away from the trough, this tropical cyclone weakened and eventually underwent extratropical transition over the open ocean, in contrast to climatological eastern North Pacific tropical cyclone behavior.Ignaciothenstrengthenedasanextratropicalcycloneduetofavorablebaroclinicconditionsandthe passage of another upper-tropospheric trough before making landfall on the northern coast of California, bringing rain to the northwestern United States. Ignacio’s remnant moisture eventually merged into a slowmoving midlatitude low pressure system that developed after interacting with the extratropical remnant of Hurricane Guillermo.

Tropical Cyclogenesis Detection in the North Pacific Using the Deviation Angle Variance Technique

AbstractThe deviation angle variance technique (DAV-T) for genesis detection is applied in the western and eastern North Pacific basins. The DAV-T quantifies the axisymmetric organization of cloud clusters using infrared brightness temperature. Since axisymmetry is typically correlated with intensity, the technique can be used to identify relatively high levels of organization at early stages of storm life cycles associated with tropical cyclogenesis. In addition, the technique can be used to automatically track cloud clusters that exhibit signs of organization. In the western North Pacific, automated tracking results for the 2009–11 typhoon seasons show that for a false alarm rate of 25.6%, 96.8% of developing tropical cyclones are detected with a median time of 18.5 h before the cluster reaches an intensity of 30 knots (kt; 1 kt = 0.51 m s−1) in the Joint Typhoon Warning Center best track at a DAV threshold of 1750°2. In the eastern North Pacific, for a false alarm rate of 38.0%, the system detects 92.9...

Automatic Tracking of Pregenesis Tropical Disturbances Within the Deviation Angle Variance System

The deviation angle variance (DAV) method is an objective tool for estimating the intensity of tropical cyclones (TCs) using geostationary infrared (IR) brightness temperature data. At early stages in TC development, the DAV signal can be also a robust predictor of tropical cyclogenesis. However, one of the problems with using the DAV method at these early stages is that the operator has to subjectively track potentially developing cloud systems, sometimes before they are clearly identifiable. Here, we present a method that allows us to automatically track the evolution of cloud clusters using only the raw IR imagery and the resulting DAV maps. We have compared our objective method with results manually obtained on a limited data set spanning a 12-day period during the 2010 hurricane season in the western North Pacific and tuned the performance of the method to the manual results. The performance of the method was then tested by comparing the results with best track and invest files produced by the Joint Typhoon Warning Center for the four-year period 2009-2012. The long-term results agree well with the best track and invest files for the disturbances analyzed in terms of start time, end time, and locations of disturbances. The automatic tracking method presented in this letter may be used to reduce the dependence of tropical cyclogenesis DAV analyses on the expertise and ability of the operator.