Sixteen years of typhoon data were studied, in an effort to develop a technique for forecasting tropical cyclone intensity changes in the Northwestern Pacific. The data base provided average changes for 24 and 48 hour periods along with the average duration of each phase (intensifying and dissipating). Further study revealed that the upper-level outflow patterns provide a means to adjust these average changes so a more realistic forecast could be generated for the individual storms. Forecasts were further improved by studying how land and other environmental features effect the life cycle of tropical cyclones. Results from the research were compiled and incorporated into a series of flow charts. These charts were created to enable individuals to quickly determine future intensities of cyclones given the storm's history and a current satellite picture. (emk).

This proposed study examines the potential use of satellite passive microwave rainfall measurements derived from Special Sensor Microwave/Imager (SSM/I) radiometers onboard the Defense Meteorological Satellite Program (DMSP) constellation to improve eastern North Pacific Ocean tropical cyclone intensity change forecasting techniques. Relationships between parameters obtained from an operational SSM/I-based rainfall measuring algorithm and 12-, 24-, 36-, 48-, 60- and 72-hour intensity changes from best track data records are examined in an effort to identify statistically significant predictors of intensity change. Correlations between rainfall parameters and intensity change are analyzed using tropical cyclone data from three years, 1992 to 1994. Stratifications based upon tropical cyclone intensity, rate of intensity change, climatology, translation, landfall and synoptic-scale environmental forcing variables are studied to understand factors that may affect a statistical relationship between rainfall parameters and intensity change. The predictive skill of statistically significant rainfall parameters is assessed by using independent tropical cyclone data from another year, 1995. In addition, case studies on individual tropical cyclones are conducted to gain insight on predictive performance and operational implementation issues.

One of the problems of concern to the tropical cyclone forecaster is forecasting the future intensity (maximum wind) of tropical cyclones. The purpose of this report is to familiarize the forecaster with the geographic and seasonal variations of tropical cyclone intensity changes based on 25 years of tropical storm and typhoon data. Intensity changes for 12, 24, and 48 hours have been examined and the results are presented. The data used for this study were extracted from a history file of tropical storms and typhoons of the western North Pacific from 1945-1969.

Up-to-date results of recent tropical cyclone research at Colorado State University are presented. Particular attention is paid to new findings which impact on tropical cyclone analysis and forecasting efforts. Observational studies using large amounts of composited rawinsonde, satellite, and aircraft flight data have been performed to analyze global aspects of tropical cyclone occurrences, physical processes of tropical cyclone genesis, tropical cyclone intensity change, environmental factors influencing tropical cyclone turning motion 24-36 hours before the turn takes place, tropical cyclone intensity determination from upper tropospheric reconnaissance, and the diurnal variations of vertical motion in tropical weather systems. (Author).

The largest errors in tropical cyclone intensity forecasting are usually the result of rapid intensification events, where rapid intensification is defined as a change in minimum central pressure of at least 42 hP sub a in a 24 hour period, or a satellite-inferred increase in maximum sustained winds of a least 23 m/s 1 per day when no measurement of central pressure is possible. An observational and theoretical study is made of the unique characteristics of rapidly intensifying typhoons in the western North Pacific. Climatological data, digital infrared satellite imagery and composited rawinsonde sounding data within 5 deg of the center of tropical cyclones were used to identify the distinctive features associated with rapid intensifiers when compared to other stratifications of non-rapid intensifiers and non-intensifiers. Rapid intensity change is indicated on satellite imagery as an extreme concentration of convection near the cyclone center. Relative concentrations of inner and outer deep cumulus convection reveal a predictive relationship between the ratio of inner core to outer core convection and the onset of rapid intensity change 12 hours later. This prediction technique was found to successfully forecast rapid or non-rapid intensification in over 90% of the cases in a three-year study of 70 northwest Pacific tropical cyclones. A physical explanation of the likely processes associated with rapid intensification is also presented. Rapid intensification is believed to be the result of weak asymmetrical wind flow across the cyclone at upper levels of the troposphere. Rapid intensifiers are shown to have large warm anomalies near the tropopause and weak vertical shear of tangential winds below 150 hP sub a. Theses. (jhd).