Tropical Cyclone Track Prediction Research Articles

Forecasting Tropical Cyclone Recurvature. Part I: Evaluation of Existing Methods

Abstract The ability of three objective tropical cyclone track prediction aids and of the official forecast to indicate that recurvature will occur within 72 h is evaluated. Recurvature is defined as the change of direction from northwest through north to northeast. For the recurvers, the timing of recurvature is assessed within 12-h categories. The evaluation of a homogeneous set of 366 western North Pacific forecasts from 1979 to 1984 provides a standard of comparison for measuring the relative skill of a new objective recurvature prediction technique in Part II of this study. The one-way influence tropical cyclone model is shown to have the highest skill in predicting recurvature for this sample.

Lagged-Average Predictions of Tropical Cyclone Tracks

Abstract The lagged-average technique of combining a set of forecasts verifying at the same time is applied to tropical cyclone track prediction. Only a 3% improvement is achieved when the 24-b one-way tropical cyclone model (OTCM) forecasts are combined with unmodified track predictions verifying at t + 24 h. After statistically modifying the previous OTCM forecasts to take into account more recent information, the mean errors of the 24-h lagged-average forecast are reduced by 15% compared to the original 24-h OTCM. The departure of the 24-h OTCM forecast from the modified lagged-average forecast appears to be a useful predictor of whether the 24-h forecast errors will be below average, average, or above average. Thus, the lagged-average forecast approach appears to be useful for tropical cyclone track prediction.

Time Consistency of Track Prediction Aids for Western North Pacific Tropical Cyclones

Abstract The time consistency of three tropical cyclone track prediction aids available at the Joint Typhoon Warning Center (JTWC), Guam is examined by comparison of successive cross-track and along-track errors relative to the best track (postseason analysis) positions. The cross-track errors are divided into three groups (terciles) that are referred to as Left, Center or Right categories. Generally, the aids have more time consistency when the error in the previous forecast is in the Right category than in the Left category. A forecast verification within the Center category of 24-b path errors generally is followed by equal chances of Left, Center or Right error categories within 24–48 h. The One-way influence Tropical Cyclone Model (OTCM) provides the most consistent forecasts in time. In general, the Climatology and Persistence (CLIPER) 24-h verification provides little information as to how the subsequent CLIPER forecast wig verify. The wobble about the actual track is defined as the difference in c...

Tropical Cyclone Track Prediction with a Barotropic Spectral Model

A barotropic spectral model (BSM) is developed to investigate the possibility of forecasting tropical cyclone tracks with global, general circulation models. The model is governed by a barotropic vorticity equation in spherical coordinates which is solved wing a spectral method with spherical harmonic basis functions. The model was run with a triangular truncation of 128 on half of the northern hemisphere (180°W–0°W), and was initialized using horizontal winds from the NMC analyses vertically averaged from 1000 to 100 mb. The storm circulation is represented by a specified axisymmetric vortex and the model was tested by making 30 track forecasts of Atlantic tropical cyclones (13 storms) which occurred from 1979 to 1984. The skill of the model was assessed by comparing the track forecasts to forecasts from a model based on climatology and persistence (CLIPER). The BSM has statistically significant skill for 24 and 36 h track forecasts and longer range of skill for forecasts of low-latitude storms. For low-latitude storms, the BSM had than the operational SANBAR and moveable fine mesh (MFM) models. The sensitivity of the model to the horizontal resolution is tested. These results suggest that track forecasts could be made with a global spectral model with a triangular truncation of about 96. It might then be feasible to make track forecasts with a global spectral model similar to the operational model at the European Centre for Medium Range Weather Forecasts which uses a triangular truncation of 106. The sensitivity of the model to the domain sin and to the specification of the initial vortex is also investigated. These results show that when simple lateral boundary conditions are used, the track forecast errors rapidly increase when the model domain is made smaller than half of a hemisphere. These results also show that the track errors are very insensitive to the size of the vortex, provided that the vortex is not unrealistically large. When the shape of the vortex profile is changed to include an anticylonic circulation at large radii, the track errors are smallest when the total angular momentum of the vortex is close to zero. The errors rapidly increase as the total angular momentum becomes negative. The effect of modifying the initial analyses so that the deep-layer mean wind in the storm region is consistent with the previous storm motion is also studied. The track errors show the most reduction when the analyses within a radius of about 1000 km of the norm am modified.

A Statistical-Climatological Tropical Cyclone Track Prediction Technique Using an EOF Representation of the Synoptic Forcing

Abstract An empirical orthogonal function (EOF) analysis is performed on a series of 504 normalized D-value fields at 500 mb. Each field is defined on a 120-point grid that is centered on the geographical position of a tropical cyclone. The EOF representation (eigenvectors) of the environmental flow field requires less than 10% of the storage needed for the original grid points. Each eigenvector represents a distinctly different synoptic-scale forcing pattern for the tropical cyclone motion. Statistical regression equations are developed to predict the zonal and meridional displacements of the tropical cyclone at 12 h intervals to 84 h. The EOF coefficients are used to represent the synoptic-scale forcing in the equations. The track forecast errors are competitive with other statistical schemes. The average displacement errors in an independent sample were ∼15% smaller than the official Joint Typhoon Warning Center forecasts. Thus, the EOF-based regression approach provides a simple and low cost technique...