Equilibrium Translation Model—A Key to Tropical Hurricane Development

The paper relates to problem of forecasting of rapid changes of tropical hurricane (TH) intensity. Challenges with description of TH development highlight pressing contemporary interdisciplinary problem of proper combination of numerical methods with adequate qualitative physical models. Previously developed equilibrium translation model (ETM) bridges this gap through introduction of physically transparent concept leading to establishment of simple relationship between main integral dynamical and thermal parameters of combined ocean-atmosphere system at the stage of TH intensification. According to ETM TH development essentially depends from a degree of conformity of thermal and dynamical environmental fields (together with high thermal potential of ocean upper layer). TH always is subjected to action of specific thermal driving mechanism with rather strong feedback tending to establish certain equilibrium between translation and heat removal. Corresponding equilibrium translation mode is considered as condition for maximum intensification of TH that is identified as alignment effect. It is assumed that alignment effect occurs at certain constant value of heat involvement factor (equal to the share of hurricane heat potential (HHP) removed by TH from an ocean during full passage of the given area). Establishment of equilibrium translation is linked to certain constant value of dimensionless alignment number. In the framework of refined version of realization of ETM (fitted to regular standard forecast advisories) this value is defined by the equality: Nal = (UtrQ)/(qR*34)=25 (where Utr is TH back boundary translation speed at tangent velocity 34 knots; Q is HHP; R*34 is so-called effective radius of TH at tangent wind velocity 34 knots (17.5 ms-1); q is average inside R34 integral (sensitive and latent) heat flow from sea surface to TH). As the most representative examples, observed in 2004 four cases of unpredicted rapid intensification are considered (cyclone FAY, TH ALEX and CHARLEY, super typhoon MA-ON). According presented analysis alignment effect has played main role in all cases under examination. Besides, in the cases of TH ALEX and CHARLEY and super-typhoon MA-ON rapid intensification has occurred against significant reduction of HHP along TH track. Simultaneously, predicted by standard regular forecast advisories courses of events qualitatively have differed from real forthcoming development. The results of the analysis clearly demonstrate fundamental character of alignment effect. Overlooking of the effect by existing forecasting models poses urgent problem of these qualitative refinement. It also deserves of close attention revealed potential for immediate performance evaluation of standard regular predictions in real time regime. In general, further development of ETM is connected with rather wide R&D activities requiring international cooperation. Unfortunately some artificial obstacles have prevented proper international publishing of initial paper on ETM in 2003. As a consequence, real opportunity was lost of before-the-fact establishment of high probability of rapid intensification of TH CHARLEY through its approaching Florida Peninsula. Initial and other articles on subject matter are displayed at web page http://gtu.ge/usr/ishekriladze/ (section - "Hurricane").