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Tropical Cyclone Research and Review  
  Tropical Cyclone Research and Review--2012, 1 (1)   Published: 2012-02-15
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Can the Extreme Rainfall Associated with Typhoon Morakot (2009) Happen in Hong Kong?

S.T. Chan, Yiwu Huang
Tropical Cyclone Research and Review. 2012, 1 (1): 1;  doi: 10.6057/2012TCRR01.01
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Typhoon Morakot hit Taiwan in August 2009 and brought torrential rain and high death toll to the region.  The registered maximum cumulative rainfall depth approached the world record of the greatest point rainfall.  In this paper, the risk of experiencing rain episodes of similar severity in Hong Kong was assessed using the Advanced Research WRF (Weather Research and Forecast) model to simulate a direct hit of Typhoon Morakot to the city.  A number of numerical experiments were conducted by transplanting the vortex of Morakot and the associated environmental conditions to the South China Sea to study the amount of rainfall that could fall in Hong Kong.  The results revealed that the difference in the topography between Taiwan and Hong Kong alone accounted for more than 60% of the total rainfall registered in Taiwan.  The enormous land mass of China to the north of Hong Kong would also weaken Morakot rapidly upon its landfall over the south China coast, causing a shift in its track and redistribution of rainfall, and a further reduction of the rainfall amount that Hong Kong would receive.  Despite that, some experiments suggested that Hong Kong could receive nearly 800 mm of rainfall in 24 hours, a figure that would break the historical record of 697.1 mm set in 1889 in Hong Kong.

How the National Forecasting Centre in Oman Dealt with Tropical Cyclone Gonu

Juma Al-Maskari
Tropical Cyclone Research and Review. 2012, 1 (1): 16;  doi: 10.6057/2012TCRR01.02
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Tropical Cyclone Gonu affected the coastal areas of Oman during the period of 5th–7th June 2007. The low pressure system which first developed on the 1st of June 2007 southwest of India intensified slowly as it moved west north-westwards towards the coastal areas of Oman reaching a super cyclonic storm (according to IMD classifications) on the 4th of June. The storm then lost its strength well before reaching the coastal areas of Oman. Tropical cyclones very rarely reach that intensity in the Arabian Sea and seldom enter the Gulf of Oman (at least from the start of records in 1945). However, according to unpublished notes by Oman Forecasting Centre (see also Membery 2001, 2002), on 4th June 1890, a tropical cyclone brought 24 hours of torrential rain to Batinah and Muscat regions, with severe flooding and widespread damage to property. This evidence, which is not known to many, clearly shows that although cyclone Gonu might have been one of the most destructive cyclones affected Oman, it is not the only one.This paper highlights the history of tropical cyclones that affected Oman and gives details on how the Oman Forecasting Centre managed and dealt with cyclone Gonu. A situation of this type was anticipated, but encountered for the first time by both forecasters and decision makers at the Directorate General of Meteorology and Air Navigation (DGMAN). Lessons learned and measures for future decisions on how to deal with severe weather events are discussed.

Summary of Retired Typhoon within the Western North Pacific Ocean

Xiaotu Lei, Xiao Zhou
Tropical Cyclone Research and Review. 2012, 1 (1): 23;  doi: 10.6057/2012TCRR01.03
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Names have been given to tropical cyclones which raging through the western North Pacific Ocean since 1947. However, considering the disastrous impact or some extreme uniqueness quite a few typhoons have their names retired from the list. This study conducts preliminary analysis and summarizes the frequency, impact and also explains why they were retired. It shows that a total of 31 typhoons (in the western North Pacific Ocean) have been removed from the list from 1947 on, most of which retired after 2000 amounting to 20 as against 11 before 2000. Collectively, these retired typhoons have made 16843 people killed or missing and caused a heavy property loss of $45.7 billion, averaging 543 fatalities and property loss of $1.69 billion each (capping at 8000 and $10 billion respectively). Most typhoons were retired due to huge personnel and property loss. However, some others were removed for their unique feature such as developed near equator, extremely long typhoon tracks, etc. Moreover, there were some retired due to neither of the above reasons. In this connection, the study also discusses the standard of retiring typhoons.

Recent Studies on Changes in Track and Convection Associated with Tropical Cyclone Landfall

Johnny C L Chan
Tropical Cyclone Research and Review. 2012, 1 (1): 33;  doi: 10.6057/2012TCRR01.04
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As a tropical cyclone makes landfall, changes in friction and moisture as well as the presence of topography will modify the flow and subsequently the convection associated with the tropical cyclone. As a result, the distribution of potential vorticity tendencies will be modified, which then leads to track deviations. Modifications of the flow will also lead to changes in the vertical wind shear and hence the convection distribution. It is these interactive processes that cause changes in the track and convective distributions of a tropical cyclone as it moves close to land. This paper presents an overview of some of the recent studies on the changes in track and structure associated with tropical cyclone landfall to provide evidence of these physical processes.

A Review on the Long Term Variations of Tropical Cyclone Activity in the Typhoon Committee Region

Tsz-cheung Lee
Tropical Cyclone Research and Review. 2012, 1 (1): 41;  doi: 10.6057/2012TCRR01.05
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A review on the long term variations of tropical cyclone (TC) activity in the Typhoon Committee region was conducted based on the assessments of IPCC, IWTC and ESCAP/WMO Typhoon Committee and a number of recent publications. The results reveal strong inter-annual and inter-decadal variations in the TC activity over the western North Pacific (WNP). Analysis of available TC data since 1950s indicates that most of the TC datasets depict a decreasing trend, and some statistically significant, in the annual number of TCs and typhoons in the WNP. For TC intensity, differences in TC databases for the WNP do not allow a convincing detection of a long term trend in this basin. Climate model projections suggest a noticeable decrease in the frequency of the WNP TCs in the 21st century. Some of the model simulations also report an increase in the number of intense TCs and the TC potential intensity in the WNP in a warmer climate. Looking forward, data homogeneity in TC databases and uncertainties in model simulation are two main hurdles hindering the determination of the past and future trends of TC activity in this basin. Inter-agency co-operations are urgently required to improve the homogeneity and consistency of TC databases in the WNP. Continuous research would also be needed to further improve our understanding of the influence of natural variability and anthropogenic warming on the TC activity in the WNP.

Tropical Cyclone Information Provided by the RSMC Tokyo-Typhoon Center

Masashi Kunitsugu
Tropical Cyclone Research and Review. 2012, 1 (1): 51;  doi: 10.6057/2012TCRR01.06
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The RSMC Tokyo - Typhoon Center provides the ESCAP/WMO Typhoon Committee Members with tropical cyclone (TC) information to support their disaster mitigation activities. Good knowledge and use of the information lead to appropriate and effective TC monitoring and warnings. Progress and future plans of TC information and products provided by the Center are presented.

Recent Progress in Urban Flood Risk Management in the Typhoon Committee Area

Zhiyu Liu
Tropical Cyclone Research and Review. 2012, 1 (1): 60;  doi: 10.6057/2012TCRR01.07
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The typhoon region is urbanizing rapidly with the increasing trend of population and economy. Fast urban development has also brought many potential troubles, and urban flooding is one of the most serious. Many aspects of urban areas are vulnerable to flood disasters and climate change. How to minimize losses caused by urban floods and harmonize relationship between floods and socio-economic development has been a significant problem that governments and international organizations work on. In recent years, risk management ideas have been introduced into flood management in the Typhoon Committee Area (TCA). This paper presents a brief review of urban flood issues and flood management in the TCA, and identifies good practices and research progress of urban flood risk management from the model cities study. In addition, some ideas about the improvement of urban flood risk management are also discussed in the paper.

Prediction of Storm Surges in the Bay of Bengal

Shishir K. Dube
Tropical Cyclone Research and Review. 2012, 1 (1): 67;  doi: 10.6057/2012TCRR01.08
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The destruction due to storm surge flooding is a serious concern along the coastal regions of the countries around the Bay of Bengal. About 300,000 lives were lost in one of the most severe cyclones that hit Bangladesh (then East Pakistan) in November 1970. More recently the Nargis cyclone of May 2008 killed about 140,000 people in Myanmar as well as caused enormous property damage. Thus, provision of precise prediction and warning of storm surges is of great interest in the region. The main objective of the present paper is to highlight the recent developments in storm surge prediction in the Bay of Bengal and also the future plan to enhance storm surge forecasting capability in the region.

Tropical Cyclone Unusual Intensity and Structure Change in the Western North Pacific Observed by Reconnaissance Aircraft furing TPARC/TCS08 and ITOP/TCS10

Peter G. Black
Tropical Cyclone Research and Review. 2012, 1 (1): 75;  doi: 10.6057/2012TCRR01.09
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The combined Tropical Cyclone Structure (TCS-08) and THORPEX Pacific-Asia Regional Campaign (T-PARC) field programs during August and September 2008 and the combined Impact of Typhoons on the Ocean in the Pacific (ITOP) and TCS-10 field programs during August, September, and October 2010 have provided unique simultaneous observations of typhoon structure and intensity together with underlying oceanic conditions during rapid intensification and rapid decay events in the northwest Pacific Ocean basin during the tropical cyclone life cycle. A new observational strategy from aircraft reconnaissance, involving combination (‘COMBO’) deployments of Global Positioning System (GPS) dropwindsondes and Airborne eXpendable Bathythermographs (AXBTs) has allowed for simultaneous observations of TC structure and intensity while also observing oceanic eddy structure beneath the TC. This strategy, together with deployment of drifting buoys and floats ahead of the TC, has led to observations in Super-TYphoon (STY) Jangmi (2008) and STY Megi (2010) that show the ocean control over TC Rapid Intensification (RI) and Rapid Decay (RD) due to pre-existing warm and cold ocean eddy features, as well as the intensity-limiting effects of oceanic ‘cold wakes’ generated by Typhoons (TYs) Fanapi (2010) and Malakas (2010).
Observations made during ‘unusual’ track changes in TY Fanapi illustrate how the TC passes over different ocean eddy features than would have occurred with a ‘normal’ straight track. These track changes led to unusual intensity changes due to subsequent movement over a warm ocean eddy feature that led to unexpected TC intensification, and this was followed by movement over shallow ocean mixed layers that led to strong ‘cold wake’ generation. This feature of ocean control then limited Fanapi’s intensification to values well below their Maximum Potential Intensity (MPI).
In addition, ‘COMBO’ observations within pre-TC disturbances show contrasting impacts on typhoon development/non-development for cases of strong ocean control and weak environmental shear (pre-Fanapi, 2010) versus cases of weak ocean control and strong environmental shear (disturbance TCS025, 2008).

WMO Typhoon Landfall Forecast Demonstration Project (WMO-TLFDP)- Concept and Progress

Xu Tang, Xiaotu Lei, Hui Yu
Tropical Cyclone Research and Review. 2012, 1 (1): 89;  doi: 10.6057/2012TCRR01.10
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The World EXPO 2010 was successfully held in Shanghai from May to October 2010. Activities related to the EXPO were spread out in the Eastern China. To provide a better typhoon landfall forecast service for the EXPO and to demonstrate the most advanced typhoon forecast techniques in the world, the ‘WMO Typhoon Landfall Forecast Demonstration Project (WMO-TLFDP)’ began in May 2010 and will end in December 2012. It is a component of the Shanghai Multi-Hazard Early Warning System Project.
Significant progresses have been made. First, the WMO-TLFDP Training Workshop on Tropical Cyclone Forecasting was held successfully in Shanghai, China during 24-28 May, 2010. Second, a total of 13 typhoon forecast product providers have participated in the project by providing real-time forecast products. Third, typhoon track, intensity and rainfall forecasts are verified in both real time and post season manners. Fourth, products of the project are disseminated through the project’s website (http://tlfdp.typhoon.gov.cn) and the operational website of the Shanghai Typhoon Warning Center. Finally, all the data and products of named tropical cyclones since May 2010 are archived by the Regional Meteorological Center of Eastern China, which are available to research, training and capacity-building activities. It is demonstrated that current operational models are valuable in providing guidance to the forecast of not only track, but also intensity and heavy rainfall of tropical cyclones. Consensus techniques and ensemble prediction systems are promising in assisting the forecasters and decision makers to provide better tropical cyclone forecast and warning service.
The WMO-TLFDP has supported effectively the forecasters and typhoon-related weather services during the World EXPO 2010, and it will continue to promote the implementation of the most advanced typhoon forecast techniques among the members of ESCAP/WMO Typhoon Committee, which ultimately will be of benefit to other WMO Members as well.

Internal Dynamical Control on Tropical Cyclone Intensity Variability

Eric A. Hendricks
Tropical Cyclone Research and Review. 2012, 1 (1): 97;  doi: 10.6057/2012TCRR01.11
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The current understanding of internal dynamical processes responsible for tropical cyclone intensity variability is reviewed. These internal dynamic processes are small in horizontal scale and are constrained to characteristics of the vortex itself and less dependent on the environmental and oceanic conditions. Important internal dynamical processes for tropical cyclone evolution are: (i) spiral rainband dynamics, (ii) asymmetric deep convection, (iii) eye/eyewall mixing, and (iv) eyewall replacement cycles. It is shown that while there exists a reasonable understanding of these internal processes in idealized frameworks, there still remains a large gap in our understanding of these processes in the real atmosphere.  Additionally, further research is warranted on the interplay of these internal processes with each other as well as their interaction with the environment.

Opportunities for Probabilistic Forecasts of Tropical Cyclone Formations and Tracks on Intraseasonal Timescales

Russell L. Elsberry, Mary S. Jordan, Fedric Vitart, Eric A. Hendricks
Tropical Cyclone Research and Review. 2012, 1 (1): 106;  doi: 10.6057/2012TCRR01.12
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An opportunity that now exists for probabilistic forecasts of western North Pacific tropical cyclone formations and tracks on timescales of 7-30 days is demonstrated from the 51-member European Center for Medium-range Weather Forecasts 32-day ensemble predictions made once a week during the 2008 and 2009 seasons. A methodology has been developed to match the ensemble member vortices to form ensemble storms, and a weighted-mean vector motion technique is applied to generate the track. An objective validation relative to the Joint Typhoon Warning Center best-tracks is supplemented with a subjective evaluation of the quality of the agreement.
Success of the approach was first demonstrated with three intense typhoons during the 2008 season. Although some successful predictions were also achieved with some moderate typhoons and tropical storms, the early and late season typhoons and the tropical depressions were not predictable on 7-30 day timescales. Evaluation of the performance during the more active and typical 2009 season again indicated success in predicting typhoons and most of the weak tropical storms and tropical depressions. The exceptions were some multiple storm events and track bifurcation scenarios due to midlatitude  interactions.
Among the challenges to produce an operational product are the requirements to make the entire procedure more automated, more objective, and with forecaster-friendly displays.  A documentation of the reliability and of the limitations of the predictions will be helpful in gaining forecaster acceptance.

Tropical Cyclone Wind Field Determination: Challenges and Possibilities

Peter Otto
Tropical Cyclone Research and Review. 2012, 1 (1): 118;  doi: 10.6057/2012TCRR01.13
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The difficulties encountered in trying to determine the intensity of any landfalling tropical cyclone are reviewed. These difficulties are then related to the complexities observed during the landfall of Severe Tropical Cyclone Larry (2006), and possible wind speed sampling deficiencies and biases are considered for that event. Recent and expected advances in knowledge of storm structure and wind speed estimation methods suggest a need for increased documentation requirements, so that the various assumptions employed in estimating landfall intensity can subsequently be improved upon. Increases in documentary requirements may also improve the error bound determination of intensity estimates of individual events, and thus ultimately the climate record as well.

Fundamental Importance of Convective Downdrafts and Mass Recycling within the Tropical Cloud Cluster and the Typhoon-Hurricane

William M. Gray
Tropical Cyclone Research and Review. 2012, 1 (1): 130;  doi: 10.6057/2012TCRR01.14
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Most meteorologists think of the organized tropical cloud cluster and typhoon-hurricane weather system as having a strong transverse (or ‘in-up-and-out’) circulation of low-level frictionally driven inflow, upward vertical motion in cloud areas, and outflow at upper tropospheric levels. Tropical weather systems also have another fundamentally important circulation within them which is an additional ‘down-and-up’ (or downdraft-and-updraft) circulation associated with evaporating downdraft motion and mass compensating condensation upward motion. This additional ‘down-and-up’ circulation has yet to be fully recognized and fully appreciated.
This paper emphasizes the fundamental role of this additional ‘down-and-up’ circulation which must be added to the accepted ‘in-up-and-out’ basis transverse circulation to obtain a full understanding of the tropical weather system’s complete vertical circulation structure.  Only by adding this additional extra ‘down-and-up’ is it possible to make simultaneous mass, energy, and moisture budgets for this class of weather system. This additional ‘down-and-up’ (or downdraft-and-updraft) circulation is indispensible in allowing tropical systems to extract large amounts of surface energy from the oceans.

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