Heavy Rainfall Forecast Research Articles

Short-term risk forecasts of heavy rainfall

Methodologies for risk forecasts of severe weather hardly exist on the scale of nowcasting (0-3 hours). Here we discuss short-term risk forecasts of heavy precipitation associated with local thunderstorms. We use COTREC/RainCast: a procedure to extrapolate radar images into the near future. An error density function is defined using the estimated error of location of the extrapolated radar patterns. The radar forecast is folded ("smeared") with the density function, leading to a probability distribution of radar intensities. An algorithm to convert the radar intensities into values of precipitation intensity provides the desired probability (or risk) of heavy rainfall at any position within the considered window in space and time. We discuss, as an example, a flood event from summer 2000.

Oceanic Rain Rate Retrievals Using TRMM Microwave Imager Multi-channel Brightness Temperatures during the 1998 SCSMEX

The purpose of this paper is to retrieve the oceanic rain rate (RR) over waters near Taiwan and Luzon from the Tropical Rainfall Measuring Mission (TRMM) Microwave Imager (TMI) multi-channel brightness temperatures (Tbs). In addition to improving heavy rainfall forecasting by providing quantitative oceanic RR estimates and possible movement direction of Mesoscale Convective Systems (MCSs), another objective of this paper is to overcome the lack of oceanic conventional observations in heavy rainfall forecasting during the Mei-Yu season. Rainfall caused by MCSs during the 1998 South China Sea Monsoon Experiment (SCSMEX) was studied using TMI nine-channel Tbs, the hourly RR from ground rain gauges, and Geostationary Meteorological Satellite (GMS) infrared (IR) Tbs. In this paper, the domain ranges from 110°E to 130°DE and from 15°N to 30°N. Two oceanic RR retrievals taken on 3 June 1998 are shown and examined. The results show that a TMI nine-channel Tbs-RR equation can retrieve the amounts of heavy rainfall caused by the MCSs that often occur during the summer monsoon season in southeastern China, the northern part of the South China Sea, Luzon, and southern Taiwan. The RR retrievals were quantitatively consistent with the rainfall observations made on nearbyislands. The GMS IR Tb 240K isotherms included most of the TMI microwave (MW) Tbs retrieved rainfall region. The heaviest rainfall region wasmore or less included in the area where the IR Tb was colder than 210K. The region had a tendency to be concentrated in the forward part of the MCS in the direction of its movement. Moreover, analyses of the rainfall events that occurred in southern Taiwan during the SCSMEX period show that there was local rainfall enhancement caused by the orographic features of the island.

An Experiment Using NSCAT Winds in the Numerical Prediction of Tropical Mesoscale Rainfall Systems under the influence of terrain

The rich mesoscale information in NSCAT winds over tropical coastal regions is used in numerical simulations of two June 1997 monsoonal cases occurring over Taiwan. It is shown that transient NSCAT mesoscale information over a localized area as small as 120 km × 240 km can result in significant improvement in the 24 h heavy rainfall forecast due to its effect on monsoonal convection and terrain effects.

An Objective Approach for Making Heavy Rainfall Forecasts Based on Numerical Model Output and the Latest Observation

An approach is presented that can make an objective heavy rainfall forecast based on numerical model output and the latest observed rainfall without employing historical data. The idea of the approach is that the mean rainfall intensity R at more than 600 grid points can be obtained from the past 6-h rainfall observations at about 700 stations, the mean vertical velocity ωRT can be derived from R, and then the change of the ωRT is calculated;finally the rainfall forecast can be made by using the changed ωRT, the model-predicted u, υ, ω, and specific humidity q. The verification shows that the forecast skill of the approach was better than that of the model during the summer seasons of 1994 and 1995.

Distant effect of monsoon depressions- Part I: Effect of formation of depressions on rainfall activity along the west coast of India

At the time of formation of monsoon depressions over northwest/head Bay fore casters generally issue heavy rainfall forecast for the Konkan-Karnataka coasts; but heavy rainfall is not realised in all cases, In this paper we have analysed all the 111 depressions that formed over northwest/head Bay during the period 1956-75 with a view to identify the synoptic differences between the occasions when the monsoon depression forming over the Bay, increases the rainfall activity over the Konkan-Karnataka coasts and when it does not.

Forecasting heavy rainfall over Delhi and neighbourhood

The wind field and the convergence pattern over Delhi have been examined with a view to develop criteria for forecasting heavy rainfall over Delhi and neighbourhood. The study reveals that on many occasions there is passage of a wave trough or rise in the rate of convergence in the lower levels 24 to 36 hours prior to the occurrence of heavy fall. It is suggested that these can be taken as guide to heavy rainfall forecasting.