Track prediction of very severe cyclone ‘Nargis’ using high resolution weather research forecasting (WRF) model

Abstract

The recent very severe cyclonic storm (VSCS) 'Nargis' over the Bay of Bengal caused widespread destruction over Myanmar after hitting the coast on 2 May 2008. The real time forecasting of the VSCS 'Nargis' was a very difficult task as it did not follow the normal westerly/northwesterly track. In the present study, a detailed diagnostic analysis of the system 'Nargis' is carried out initially to investigate the features associated with this unusual movement and subsequently the real time forecast of VSCS 'Nargis' using high resolution advanced version weather research forecasting (WRF) model is presented. The advanced research WRF model was run for 72 h at 27 km and 20 km resolutions with 28, 29, 30 April and 1 May as the initial conditions. The diagnostic study indicates that the recurvature of the system 'Nargis' was mainly associated with:• upper level southerly/southwesterly steering wind at 200 hPa level associated with anticyclonic circulation over southeastern sector of the centre of the system, • higher SST (29 • C or more) with higher positive anomalies over the region to the northeast of the cyclone centre, and • large negative 24 h pressure changes and large vorticity maximum to the east of the system.The real time track forecast using the WRF model run at 27 km and 20 km resolution based on the initial conditions of 28 April (when the system was only 550 km away from the Indian coast) indicated that the system had a northeasterly forecast track and was not expected to cross the Indian coast. Similarly, based on 29 April initial condition the system showed east/east-northeasterly movement towards the Myanmar coast. The east/east-northeasterly movement of the 'Nargis' was persisting in the forecast based on 30 April and 1 May initial conditions with respective landfall errors of 85 km and 50 km with 27 km resolution, which reduces to 30 km and 40 km respectively with 20 km resolution, however, with a landfall time delay of about 10 h. Improvement of mean forecast errors at different forecast hours is noticed in WRF model run at higher resolution compared to that run at lower resolution. Thus, it is very clear that the advanced version WRF model had captured movement of the system reasonably well almost 3 days in advance. Consistence with the diagnostic analysis the WRF model forecast also indicates southerly/southwesterly strong steering wind at 200 hPa level and maximum pressure fall to the east of the system.

Effect of tropical cyclones on the tropical tropopause parameters observed using COSMIC GPS RO data

“…This system moved slightly north-eastwards and intensified into a cyclone at 00:00 UTC of 28 April. It remained stationary for some time and further intensified into an SCS at 09:00 UTC on 28 April and into a VSCS grade, as classified by the IMD, at 03:00 UTC on 29 April (Pattnaik and Rama Rao, 2008). It moved further eastward and crossed the coast of Myanmar on 2 May at 06:00 UTC.…”

“…India has a long coastline, which is prone to very severe cyclone formations in the Arabian Sea (AS) and the Bay of Bengal (BoB). Over the Indian region, these TCs occur during the pre-monsoon (April-May), early monsoon (June) and post-monsoon (September-November) seasons (Pattnaik and Rama Rao, 2008). They persist for a few days to weeks and have large convective activity around the eye, with a horizontal scale of hundreds of kilometres.…”

Effect of tropical cyclones on the stratosphere–troposphere exchange observed using satellite observations over the north Indian Ocean

“…The TCs over the north Indian Ocean are classified into different categories by IMD based on their maximum sustained wind speed. They are classified as (1) low pressure when the maximum sustained wind speed at the sea surface is < 17 knots (32 km h −1 ), (2) depression (D) at 17-27 knots (32-50 km h −1 ), (3) deep depression (DD) at 28-33 knots (51-59 km h −1 ), (4) cyclonic storm (CS) at 34-47 knots (60-90 km h −1 ), (5) severe cyclonic storm (SCS) at 48-63 knots (90-110 km h −1 ), (6) very severe cyclonic storm (VSCS) at 64-119 knots (119-220 km h −1 ), and (7) super cyclonic storm (SuCS) at > 119 knots (220 km h −1 ) (Pattnaik and Rama Rao, 2008). Table 2 shows the different cyclones used in the present study and their maximum intensity, sustained time, and sustained time for the peak intensity period of each cyclone.…”

Simulation of the Structure and Track of the Tropical Cyclone Sidr using Numerical Models

“…Mohanty et al [2] used MM5 model to simulate the Orissa super cyclone (1999). Again, WRF model has also been used in a number of studies for the simulation of tropical cyclones [3,4]. There are a number of comparative studies on the performance of the mesoscale models for severe weather events triggered by convection.…”