Search Results

You are looking at 1 - 10 of 19 items for

  • Author or Editor: Charles J. Neumann x
  • Refine by Access: All Content x
Clear All Modify Search
Charles J. Neumann

Abstract

No abstract available

Full access
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.

Full access
Charles J. Neumann

Abstract

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.

Full access
Charles J. Neumann

Abstract

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.

Full access
Charles J. Neumann

Abstract

Full access
Keqin Dong and Charles J. Neumann

Abstract

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.

Full access
Keqin Dong and Charles J. Neumann

Abstract

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.

Full access
Lloyd J. Shapiro and Charles J. Neumann

Abstract

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.

Full access
Charles J. Neumann and Elie A. Randrianarison

Abstract

The derivation of a system of regression equations for the prediction of tropical cyclone motion over the Southwest Indian Ocean is described. The equations use the same predictors that are typically used as storm selection criteria by analog models. In this sense, the prediction model simulates an analog forecast. To complete the simulation, a method is described whereby the prediction errors (residuals) of the development data are used to construct equi-probability ellipses similar to those used by analog models. Testing the prediction equations on three years of independent data for the years 1970, 1971 and 1972 indicates a forecast accuracy closely approximating that realized by a similar system of prediction equations in operational use in the Atlantic.

Full access
Charles J. Neumann and Joseph M. Pelissier

Abstract

This study provides an operational evaluation of the seven prediction models-five statistical and two dynamical-used at the National Hurricane Center. Following a brief description of the rationale for each model, various performance characteristics, including forecast error, skill. bias. dispersion, timeliness and availability are evaluated.

The conclusion of the study is that none of the models can be singled out as clearly superior or inferior, each having at least one temporal, spatial, economic or utilitarian advantage. In practice, it is difficult to combine these advantages into one all-purpose model. Accordingly. for some time to come, operational guidance will be obtained from a number of different models, both statistical and dynamical. Tropical cyclone forecasters will need to be kept aware of model attributes so that potential conflicts in the guidance can be rationally resolved.

Full access