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Five statistical and dynamical tropical cyclone intensity guidance techniques available at the National Hurricane Center (NHC) during the 2003 and 2004 Atlantic and eastern North Pacific seasons were evaluated within three intensity phases: (I) formation; (II) early intensification, with a subcategory (IIa) of a decay and reintensification cycle; and (III) decay. In phase I in the Atlantic, the various techniques tended to predict that a tropical storm would form from six tropical depressions that did not develop further, and thus the tendency was for false alarms in these cases. For the other 24 depressions that did become tropical storms, the statistical-dynamical techniques, statistical hurricane prediction scheme (SHIPS) and decay SHIPS (DSHIPS), have some skill relative to the 5-day statistical hurricane intensity forecast climatology and persistence technique, but they also tend to intensify all depressions and thus are prone to false alarms. In phase II, the statistical-dynamical models SHIPS and DSHIPS do not predict the rapid intensification cases (Ն30 kt in 24 h) 48 h in advance. Although the dynamical Geophysical Fluid Dynamics Interpolated model does predict rapid intensification, many of these cases are at the incorrect times with many false alarms. The best performances in forecasting at least 24 h in advance the 21 decay and reintensification cycles in the Atlantic were the three forecasts by the dynamical Geophysical Fluid Dynamics Model-Navy (interpolated) model. Whereas DSHIPS was the best technique in the Atlantic during the decay phase III, none of the techniques excelled in the eastern North Pacific. All techniques tend to decay the tropical cyclones in both basins too slowly, except that DSHIPS performed well (12 of 18) during rapid decay events in the Atlantic. This evaluation indicates where NHC forecasters have deficient guidance and thus where research is necessary for improving intensity forecasts.

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Public reporting burden for this collection of information is estimated to average I hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection ofinformation, including suggestions for reducing this burden, to Washington Headquarters Services, Directorate for information Operations and Reports, 1215 Jefferson Davis Highway, Suite 1204, Arlington, VA 22202-4302, and to the Office ofrManagement and Budget, Paperwork Reduction Project (0704-0188), Washington, DC 20503. The preliminary adaptation by Bannister et al. (1997) of the Systematic Approach to tropical cyclone (TC) track forecasting meteorological knowledge base to the Southern Hemisphere has been extended to eight seasons (1990-91 through 1997-98), which includes 145 (90) cyclones in the South Indian (Pacific) region. A total of 3257 synoptic pattern/region classifications could be described in the context of only four synoptic patterns and 11 synoptic regions. Updated track summaries in each pattern/region combination, and the recurring (more than three) environment structure transitions are provided. AGENCY USE ONLY (Refinements in the set of TC-environment transitional mechanisms in the meteorological knowledge base include: (i) new Equatorial Westerly Wind Burst Mechanism; (ii) new semi-direct TC interaction equatorward conceptual model; (iii) additional variations of the Subtropical Ridge Modulation mechanisms; and (iv) further cases of Vertical Wind Shear leading to dramatic TC track changes. These refinements are illustrated with case studies intended to assist the forecaster in recognizing these transitional mechanisms, and thus anticipating TC track changes in the Southern Hemisphere. Fig. 14 (a) NOGAPS 500-mb analysis as in Fig. 13, except valid at 00 UTC 13 33 November 1991, and (b) the GMS IR imagery at 03 UTC 13 November 1991. Fig. 15 (a) NOGAPS 500-mb analysis as in Fig. 13, except at 00 UTC 14 November 1991, 35 and the (b) GMS IR imagery at 03 UTC 14 November 1991. .40cr. Each of the TC-environment transformations (Fig. 1, lower right) originally defined for Northern Hemisphere TCs were also found by Bannister et al. (1997) to apply in the SH sample.In particular, three TC interactions (Direct, Semi-direct, and Indirect) defined in a recent paper were adapted for SH application. Series of NOGAPS analyses and tracks during TC interactions in the SH were provided in Bannister et al. (1997). An objective technique for detecting certain TC interactions developed by Carr and Elsberry (1998) for the western North Pacific was modified for SH geometry of tracks and provided useful guidance.As long as a TC remains in the environmental steering flow associated with a particular synoptic pattern and region, the motion of the TC will tend to fall within a certairr range of 4 directions and speeds, i.e., in...

The Joint Typhoon Warning Center has been issuing 96- and 120-h track forecasts since May 2003. It uses four dynamical models that provide guidance at these forecast intervals and relies heavily on a consensus of these four models in producing the official forecast. Whereas each of the models has skill, each occasionally has large errors. The objective of this study is to provide a characterization of these errors in the western North Pacific during 2004 for two of the four models: the Navy Operational Global Atmospheric Prediction System (NOGAPS) and the U.S. Navy’s version of the Geophysical Fluid Dynamics Laboratory model (GFDN). All 96- and 120-h track errors greater than 400 and 500 n mi, respectively, are examined following the approach developed recently by Carr and Elsberry. All of these large-error cases can be attributed to the models not properly representing the physical processes known to control tropical cyclone motion, which were classified in a series of conceptual models by Carr and Elsberry for either tropical-related or midlatitude-related mechanisms. For those large-error cases where an error mechanism could be established, midlatitude influences caused 83% (85%) of the NOGAPS (GFDN) errors. The most common tropical influence is an excessive direct cyclone interaction in which the tropical cyclone track is erroneously affected by an adjacent cyclone. The most common midlatitude-related errors in the NOGAPS tracks arise from an erroneous prediction of the environmental flow dominated by a ridge in the midlatitudes. Errors in the GFDN tracks are caused by both ridge-dominated and trough-dominated environmental flows in the midlatitudes. Case studies illustrating the key error mechanisms are provided. An ability to confidently identify these error mechanisms and thereby eliminate likely erroneous tracks from the consensus would improve the accuracy of 96- and 120-h track forecasts.