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Charles J. Neumann

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Charles J. Neumann

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Charles J. Neumann

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One of the major problems concerning meteorologists at the Kennedy Space Center, Fla, involves the forecasting of thunderstorm activity and associated adverse weather phenomena. The purpose of the study is to outline some of the more successful diagnostic tools which have been developed to aid the forecaster. These involve a variety of statistical procedures including conditional probabilities, exposure-period probabilities, and systems of multiple-regression equations based on nonlinear predictors.

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Charles J. Neumann

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The occurrence of large surface hail is extremely rare in low latitudes. In an effort to explain this deficiency, this paper presents a mesoscale analysis of an isolated case of large hail over Miami, Florida, in March 1963. For this analysis, a dense network of hail size and frequency sensors was conveniently provided by the hall-punctured overhead portions of the many screened patio and swimming pool enclosures which are part of the Miami environment. A study of this damage pattern along with considerable mesosynoptic data on pressure, rainfall and wind revealed intimate details of the storm's behavior and showed that it displayed many of the features generally associated with Midwest tornadic hailstorms.

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Charles J. Neumann

Errors in official 24 h forecasts of tropical cyclone motion over the Atlantic for the period 1954–80 are examined for the purpose of isolating any long-term trends in the data. It is shown that the magnitude of a forecast error has been primarily a function of forecast difficulty, i.e., how well storm motion adheres to climatology and persistence. Another contributing factor (in the negative partial correlation sense) is shown to be the storm's initial longitude—a measure of the adequacy of initial analyses.

After adjusting 24 h forecast error for these two factors, it is shown that errors have declined gradually over the 27 years from near 124 n mi in 1954 to near 107 n mi in 1980—a 13.7% reduction. Most of the decline since the mid-1960s is attributed to better specification of initial storm motion through satellite imagery.

Although the decline of forecast errors is encouraging, a disturbing aspect is that the rate of decline appears to have slowed in recent years. This leveling-off is attributed to a loss in the ability to assess environmental steering through mid-level analysis deficiencies that have been compounding since 1965 and, more recently, to a plateauing in the ability to obtain still better storm initial-motion vectors. To assure a continued monotonic decline in 24 h forecast errors, mid-level initial analysis (500 mb) over the essentially data-void tropical cyclone basins must be improved.

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Keqin Dong and Charles J. Neumann

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Based on 920 cases, the relationship between Atlantic tropical cyclone motion and environmental geostrophic flows at ten levels (from 1000 to 100 mb) has been calculated and analyzed. For the average situation, it is shown that the steering relationship is considerably different between higher and lower tropospheric levels, and between easterlies and westerlies. Also, there are some differences in an optimal statistical steering function between different storm developmental states. The results of a further correlation and regression analysis of these same data show that the height of the optimum single steering level for hurricanes is higher than that for tropical storms.

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Keqin Dong and Charles J. Neumann

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The interaction between spatially proximate (binary) tropical cyclones is such that relative rotation in the counterclockwise sense and decreasing separation distance between the two storm centers can be expected. This is referred to as the Fujiwhara effect. This study analyzes this effect for 43 binary tropical cyclone systems which occurred over the western North Pacific, 1949–78. It is shown that most demonstrated mutual interaction according to Fujiwhara expectations. However, there were notable apparent exceptions.

Further analysis of these exceptional cases shows that environmental currents in which the storms were embedded had a significant effect on relative motion and masked the Fujiwhara effect. Additionally, it was found that storms exhibiting behavior most in accordance with Fujiwhara expectations were located in or near the Intertropical Convergence Zone. The main conclusion of the study, in confirmation of earlier studies, is that forces relative to environmental steering must be determined and filtered before one can determine forces attributable to the Fujiwhara effect alone.

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Lloyd J. Shapiro and Charles J. Neumann

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Statistical models for the prediction of tropical cyclone motion traditionally have been formulated in a coordinate system oriented with respect to zonal and meridional directions. An investigation is made here into the forecast error reducing potential of a grid system reoriented with respect to initial storm heading. The developmental data comprise Atlantic forecast situations from 1965 through 1980 on all storms initially north of about 25°N. Reorientation of the coordinate system reduces the total variance in 24 h storm motion by 40%, projects most of the motion onto one (along-track) component of displacement, and makes the components nearly independent of each other. For 48 and 72 h displacements, however, these advantageous effects are substantially diminished or eliminated.

Synoptic predictors derived from current deep-layer mean heights on a grid of 1700 km radius are used to forecast storm displacements. For the developmental data, grid reorientation lowers the 24 h forecast error by 13%, and reduces the slow speed bias by a factor of 2/4. For 24 h forecasts the skill in the prediction of cross-track motion is small. Empirical Orthogonal Function and Principal Estimator Patterns provide insight into the role of reorientation in the reduction of forecast error, and the position of grid-point height predictors selected by a screening technique.

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JOHN R. HOPE and CHARLES J. NEUMANN

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The HURRAN (hurricane analog) technique for selecting analogs for an existing tropical storm or hurricane is described. This fully computerized program examines tracks of all Atlantic tropical storms or hurricanes since 1886, and those that have designated characteristics similar to an existing storm are selected and identified. Positions of storms selected as analogs are determined at 12, 24, 36, 48, and 72 hr after the initial time. Probability ellipses are computed from the resulting arrays and plotted on an x, y (CALCOMP) offline plotter. The program also has the option of computing the probability that the storm center will be located within a fixed distance of a given point at a specific time. Operational use of HURRAN during the 1969 hurricane season, including both its utility and limitations, is described.

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Charles J. Neumann and Miles B. Lawrence

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Current statistical models for the prediction of tropical cyclone motion use predictors derived from climatology, persistence, and observed geopotential height data. This paper describes an operational experiment conducted during the 1973 and 1974 Atlantic hurricane seasons whereby prognostic 500 mb height data from the National Meteorological Center's primitive equation model were also included as statistical predictors.

Both the “perfect-prog” and a “simulated-model-output-statistics” (SMOS) approach were utilized to introduce the prognostic height data into the statistical prediction equations. Compared to the current “state-of-the-art” of tropical cyclone forecasting, the perfect-prog technique gave relatively poor displacement forecasts for the first half of the 72 h forecast period but excellent forecasts for the latter half. The SMOS method performed well over the entire period but the 72.h displacement error was somewhat greater than that of the perfect-prog equations.

The results of the test are extremely encouraging and suggest that independent predictive information obtained from the numerical prognoses can be objectively used to improve the performance of current statistical tropical cyclone prediction models.

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