Storm Surge Forecasting at RSMC New Delhi Storm Surge Forecasting at RSMC New Delhi ::

Current Status and Future PlansCurrent Status and Future Plans

INDIA METEOROLOGICAL DEPARTMENTINDIA METEOROLOGICAL DEPARTMENTMAUSAM BHAVAN, LODI ROAD , NEW DELHI-110003MAUSAM BHAVAN, LODI ROAD , NEW DELHI-110003

mohapatraimd@gmail.commohapatraimd@gmail.com

M MohapatraM Mohapatra

Presentation layoutPresentation layout

IntroductionIntroduction

Storm Surge and coastal inundation Monitoring and Storm Surge and coastal inundation Monitoring and

PredictionPrediction

Storm surge and coastal inundation warning services Storm surge and coastal inundation warning services

Problem areas and ProspectsProblem areas and Prospects

ConclusionsConclusions

Impact of Cyclones

Components of sea level elevation • Astronomical Tide

• Wind waves

• Wave set up

• Storm surge

• Tsunamis

• Abnormal rise in sea level along the coast in association with a

landfalling tropical cyclone is popularly known as storm surge.

• Storm surges can be defined as oscillations of the water level in

a coastal or inland body of water in the time range of a few

minutes to a few days, resulting from forcing from atmospheric

weather systems.

• According to above definition, the so-called wind waves, which

have durations on the order of several seconds, are excluded

• (WMO,

2011).

Storm Surge

• Tides, storm surges and tsunamis belong to the class of long gravity

waves (Gonnert et al., 2001). • Storm surges are centred at about 10–4 cycles per second (cps, or

hertz, Hz), which gives a period of approximately three hours.

However, the periods of oscillations may vary considerably. • That storm surges can occur over short periods (~ a few minutes) is

generally well understood and recognized. However, the situations

in which high water levels associated with storm surge events can

last for two to three days are not.

Duration of storm surge depends on• topography of the body of water, • direction of movement of the storm, • strength of the storm, • stratification of the water body and • nature of tidal motion in the water body.

Characteristics of Storm Surge

Historical Records of Storm Surge (India)

Cyclones Storm Surge Height (m) Hooghly river (WB),7 October 1737 : 13

Contai (WB),5 October 1864 : 10-13

Paradip, Orissa,October 1971 : 4-5

Balasore, Orissa, May 1989 : 3-6

Orissa Super Cyclone, October 1999 : 5-6

The funnel-shape of the North Indian Ocean and shallow bathymetry act to focus some of the world's highest storm storms onto the low-lying area at the northern end of the Bay of Bengal.

Observational data on storm surges As part of the Indian Tsunami Early Warning System, a real time

network of Tide gauges has been established by Survey of India (SOI)

and National Institute of Ocean Technology (NIOT).

The network comprises of 50 (36 by SOI and 14 by NIOT)

Tide gauges transmitting real time data through satellite

communication to INCOIS at Hyderabad, SOI at Dehradun and NIOT

at Chennai simultaneously for processing and interpretation.

In addition, the real time tide data from the Global Sea Level

Observing System (GLOSS), in Indian Ocean is being received at

INCOIS via internet.

However, the tide gauge network is not dense enough to record the

storm surge due to cyclone always.

As a result, the storm surge at a coastal point is mainly estimated by

the post-cyclone survey team based on the saline water marks etc.

A shallower bathymetry piles up the surge more

Observational data on storm surges

Factors influencing Storm Surges They include the oceanographic and meteorological parameters

Storm characteristics

Hydrological factors,

Basin characteristics and coastal geometry,

Wind stress

Seabed friction and

Information about the astronomical tides.

DUNE

STORM SURGESTORM SURGE

DUNE

HIGH TIDE

STORM SURGE

MEAN TIDE (MSL)

LOW TIDE

Tide Surge Interaction The rise in sea level due to high tide may be as high as 4.5 metre

above the mean sea level at some parts of Indian coast.

The worst devastation is caused when peak surge occurs at the

time of high tide. When Storm surge is combined with the

astronomical tide it is called as storm tide.

The storm surge modifies the tide while the tidal cycle produces

alterations in the storm surge.

• The main causes that produce these interactions are the effects of

bottom friction and the variation of the wave propagation speed

(which is dependent on total depth).

Surge–river interaction River flows can influence considerably the development of storm

surge in the mouth of a river, where pronounced temperature and

salinity gradients are formed.

Density-driven forces interact with the motion caused by external

forces, forming a complicated dynamic system.

Surge–river interactions have been successfully modelled within a

proper mathematical formulation of motion, involving momentum, heat

and salt (WMO, 2011)

The influence of river runoff on water-level oscillations at the open

coast is relatively small. Even with very large river discharge (water

level is raised by several metres in river), influence on sea level is

quickly reduced to no more than a few tens of centimetres.

Storm surge propagation into estuaries and distance of sea water

penetration along a river depends on bottom slope of river. If river bed

is relatively flat, storm surges can propagate upstream for tens of

kilometres.

Interaction of surge and wind waves Contribution of Ocean waves to roughness of the sea surface has

been extensively studied (see, for example, Donelan et al., 1993).

There is a dependence of drag coefficient on state of development of

waves and various methods have been developed (Johnson et al.,

1998).

Traditional approaches to the determination of surface stress used

for storm surge calculations consider momentum transfer to be

solely and directly from the atmosphere to the surface current.

Increased roughness of the sea surface due to wave growth during

active stage of the storm can enhance momentum exchange, so that

water levels vary in a more physically realistic way in an atmosphere,

wave and storm surge coupled model.

Widely used wave models can provide parameters to facilitate wave–

surge coupling through surface stress (Janssen and Bidlot, 2003;

Tolman, 2002).

Interaction of surge and wave set-up

The “wave set-up” is the additional water level due to the transfer of

wave related momentum during the wave-breaking process.

The contribution of wave set-up during extreme storm events can

add up to 1 metre to the sea level.

It is normally difficult to distinguish by measurement wave set-up

from the larger-scale storm surge, since both cause sea levels to be

higher than tidal predictions and both are due to meteorological

effects.

However, estimates of the set-up component can be made from a

numerical modelling study(Brown et al, 2011)

Storm surge and Meteorological Factors • The higher the cyclone intensity, the higher the storm surge.

• Maximum storm surge occurs to the right of the storm track,

roughly at the radius of max winds.

• Very small, compact cyclones cause less storm surge than do

large-sized cyclones.

• Faster-moving cyclones cause higher surges at the coast line than

do slower-moving hurricanes.

• For areas with gentle slopes of the continental shelf, storm surge

is large but waves are small.

• Areas with deep water just offshore experience large waves, but

little storm surge. (Gray, 2005)

Storm Surge Forecasting in World Before the computer era, the techniques used for storm surge

prediction were

analytical,

empirical,

graphical (nomograms) and

statistical (regression relations).

Electrical analog methods

Various methods currently used world-wide for storm surge

prediction are as follows.

Empirical methods for surge prediction

Statistical methods

Storm surge prediction through artificial neural networks

Numerical methods

Storm Surge Forecasting in World

Operational Storm Surge Forecasting in India:Forecast Parameters

The followings are the parameters for prediction of storm surge

• Time of commencement of storm surge

• Duration

• Height of storm surge

• Area to be affected

Operational Storm Surge Forecasting in India : Methodology

Empirical and analytical methods-Nomograms

Dynamical methods-IITD model

Operational storm surge forecasting in Operational storm surge forecasting in IMDIMD

Formulation Numerical solution to hydrodynamical

equation following Jelenianski (1972)

Grid size 6.4 km

Time step 2.5 min

Bathymetry Mean bathymetry for each coastal

segment for individual basins

computed from hydrographic charts

Ghosh Model

Operational storm surge forecasting in IMDOperational storm surge forecasting in IMDGhosh Model

• The meteorological inputs are:

o Pressure drop,

o Radius of maximum winds,

o Angle of track with the coast and

o the landfall point.

• The first nomogram gives the peak surge as a function of the pressure

drop and radius of maximum winds.

• The peak surge gets modified by the shoaling and storm motion

factors defined through second and third nomograms.

• Total surge is the product of preliminary estimates of surge from the

first nomogram, shoaling factor and motion factor.

First Nomogram : Peak SurgeFirst Nomogram : Peak Surge

• Peak Surge as a Peak Surge as a Function of Function of

• Pressure drop andPressure drop and• radius of maximum windradius of maximum wind

Second Nomogram : Shoaling FactorSecond Nomogram : Shoaling Factor

Third Nomogram : Vector Storm MotionThird Nomogram : Vector Storm Motion

• InputsInputs

• Meteorological InputMeteorological Input

• Location specific inputLocation specific input

• Hydrological and Oceanographic inputHydrological and Oceanographic input

• ModelModel

• Dynamical storm modelDynamical storm model

• Wind Stress associated with Cyclones

• Storm Surge Model Equations

• Vertically Integrated Mass Continuity

• Vertically Integrated Momentum

IIT Delhi Storm Surge ModelIIT Delhi Storm Surge Model

• It is fully non-linear and is forced by wind stress and by quadratic

bottom friction.

• The analysis area of the model covers from 2 ºN to 25º N and 45ºE to

100ºE.

• A uniform grid distance is taken along latitudinal and longitudinal

direction.

• Orthogonal straight-line segments represent the coastal boundaries

in the model.

• Finite difference techniques applied to the simulation of surges.

• Smoothed bathymetry is used from the depth collected from naval

hydrographic charts.

Features of IITD Model:Features of IITD Model:

The performance of this model with respect to

Indian coast has been satisfactory.

It has been made operational in IMD and other

Panel member countries

It uses the meteorological inputs provided by IMD

However, it has some limitations

It gives residual storm surge only

Performance of IITD Model

RMAX = 40 km, DP = 98 mb COMPUTED PEAK SURGE = 2.6 mOBSERVED SURGE= 2-3 m

PAKISTAN

ARABIAN SEA

OMAN

OMARA●

JASK● KALA

K●

GWADAR●

MUSCAT●

IRAN

Surge due to Gonu

Rmax = 25 km, DP = 68 hPaObserved surge =4 - 5.5 mComputed surge = 5.8 m

● MONGLA ●

Kuakata

Surge due to SIDR

Role of Meteorological inputs for storm surge prediction

Pressure drop

Radius of Max. winds

Vector motion of the cyclone

Place of landfall Duration of the storm

Hence, proper monitoring and prediction of cyclone is very essential

• Predictions of storm surges have shorter ranges, usually 24 hrs.

• Products derived from the numerical models are diverse and include

time-varying sea level (surge) forecasts at specified locations and

also charts, including local peaks and maxima charts

• Over Indian region, the storm surge forecast is usually issued in

association with cyclone warning bulletin, every three hour

• Textual in form and is mentioned as, ‘storm surge of x meters above

astronomical tide is likely to be inundate the low lying areas of a, b,

and c districts at the time of landfall.

• Does not specify time of commencement and duration of storm

surge and amount of coastal inundation in terms of area and height

of water.

• Storm surge warning is from warning stage of cyclone.

Storm Surge Warning : Storm Surge Warning : Product disseminationProduct dissemination

Storm Surge Warning (Product dissemination)Storm Surge Warning (Product dissemination)Format for Cyclone Warning Bulletin for AIR/Press / Public Format for Cyclone Warning Bulletin for AIR/Press / Public Cyclone Alert / Warning Bulletin No. ______ issued by _____ at _____ Hrs. IST Cyclone Alert / Warning Bulletin No. ______ issued by _____ at _____ Hrs. IST on _________ (Date) for repeated broadcast at hourly / half hourly intervals.on _________ (Date) for repeated broadcast at hourly / half hourly intervals.

Cyclone Alert / Warning for _______ Districts. Cyclone centred at _____ hrs. IST Cyclone Alert / Warning for _______ Districts. Cyclone centred at _____ hrs. IST of ________ (date) about ____________ kms. ________ of (direction) of ________ (date) about ____________ kms. ________ of (direction) _______(Place). Expected to intensify further and move in a _________ direction _______(Place). Expected to intensify further and move in a _________ direction and cross _______ coast near / between ____________ (Place)________ and cross _______ coast near / between ____________ (Place)________ (day/time).(day/time). Under its influence heavy to very heavy rain/extremely heavy rain likely cause Under its influence heavy to very heavy rain/extremely heavy rain likely cause floods in _______ districts commencing from _________ (time/day). Gales speed floods in _______ districts commencing from _________ (time/day). Gales speed reaching ______ kmph causing _______ damage ________in districts reaching ______ kmph causing _______ damage ________in districts commencing from ____________ (Date/Time) Gale force winds reaching -- kmph commencing from ____________ (Date/Time) Gale force winds reaching -- kmph likely extend into _________ Districts, causing damage ___________ in likely extend into _________ Districts, causing damage ___________ in ________ districts. ________ districts. Tidal wave of ________ m Likely inundate low lying area of Tidal wave of ________ m Likely inundate low lying area of _______ Districts at the time of crossing coast. _______ Districts at the time of crossing coast.

Fishermen advised not to venture out.Fishermen advised not to venture out.Public advised to cooperate with the State authorities in disaster management Public advised to cooperate with the State authorities in disaster management efforts.efforts.

Storm Surge Warning Product DisseminationStorm Surge Warning Product DisseminationFormat for State/Central Govt. Officials/Vital installations / Registered User Format for State/Central Govt. Officials/Vital installations / Registered User

Cyclone Alert/ Cyclone Warning Bulletin No. Cyclone Alert/ Cyclone Warning Bulletin No.

Date and Time of Issue: (i)(i)Information on cycloneInformation on cyclone : The cyclonic storm lay over........Bay of : The cyclonic storm lay over........Bay of

Bengal/Arabian Sea Center........kms......(Direction) of ......... place. Bengal/Arabian Sea Center........kms......(Direction) of ......... place. (ii)(ii)ForecastForecast

Further intensification:Further intensification:Direction of Movement:Direction of Movement:Expected landfall area:Expected landfall area:Expected time of landfall:Expected time of landfall:

(iii) Weather Warning (iii) Weather Warning (a)Rainfall.........in..........Districts(Names)(a)Rainfall.........in..........Districts(Names)(b)Gales reaching.........in...........Districts(Names)(b)Gales reaching.........in...........Districts(Names)(c) Gale force winds reaching 35 knots in ................... Districts(c) Gale force winds reaching 35 knots in ................... Districts(d)(d) Tidal waves ............... in coastal areas of .................. Districts (Names)Tidal waves ............... in coastal areas of .................. Districts (Names)(e) Sea condition: (e) Sea condition: (f)Damage(As per IMD instruction).......Districts(Names)(f)Damage(As per IMD instruction).......Districts(Names)(g)Likely impacts as per IMD Monograph on “Damage Potential of Tropical (g)Likely impacts as per IMD Monograph on “Damage Potential of Tropical (iv)Advice(iv)Advice

storm surge prediction over the WMO/ESCAP Panel region.

Till 2008, RSMC, New Delhi was issuing storm surge prediction for

Indian coast only.

Based on the recommendations of WMO Expert Team to Myanmar

after NARGIS and subsequent recommendation of WMO TCP, it

has been decided to issue storm surge guidance to member

countries based on IITD model.

It has been implemented since 2009 with effect from cyclone, BIJLI

in April 2009.

Forecast Verification The performance of operational storm surge models is monitored, in most

cases, on a continuous basis.

The sea-level products considered for the validation are either complete

time series, peak levels or levels at selected times (such as high and low

waters).

The statistical parameters obtained, usually for different forecast ranges,

are varied.

The bias, RMS, standard deviation, average percentage error, linear

regression (correlation coefficient) and the relation of standard error to

mean square deviation are chosen by the different forecasting agencies.

Statistics are provided either with a monthly or yearly frequency or may

be related to the occurrence of major storms.

In IMD, the predicted peak storm surge is verified against the

observed/estimated peak surge due to a cyclone.

System Point of landfall Forecast Storm surge and area to be affected, time of issue

Actual Storm Surge and Affected Area

CS Bijli over BOB(14-17 April 2009)

Crossed Bangladesh coast as a deep depression near 22.20N and 91.80E around 1600 UTC of 17 April

No warning for storm surge No surge observed.

SCS AILA over BoB (23-26 May, 2009)

Crossed West Bengal coast near Sagar Island between 0800 and 0900 UTC of 25 May 2009

2-3 m Sagar Island and adjoining areas of West Bengal and Bangladesh, issued 21 hrs in advance of landfall time..

2-3 m Western regions of BangladeshSunderban delta

CS Phyan over the Arabian Sea (09-12 Nov., 2009)

Crossed Maharashtra coast between Alibag and Mumbai during 1000 and 1100 UTC of 11 November, 2009.

1m Sindhudurg, Raigad, Greater Mumbai and Thane districts of Maharashtra and adjoining Valsad distrist of Gujarat, issued 8 hrs in advance

No storm surge could be estimated after the landfall.

CS, Ward over Bay of BengalDec 2009)

Crossed Sri Lanka coast as a depression

No storm surge warning issued

No storm surge observed

SCS LAILA over BoB (17-21 May, 2010)

Crossed Andhra Pradesh Coast near 16.0/80.5 between 1100 &1200 UTC of 20 May

1.5 to 2.0 m Low lying areas of Guntur Krishna East and West Gidavari Districts, issued 33 hrs before landfall

2- 3 m, near Surya Lanka (near Baptla)

Forecast Verification in IMD

System Point of landfall Forecast Storm surge above astronomical tide and area to be affected, time of issue

Actual Storm Surge and Affected Area

VSCS, Phet over Arabian Sea (31 May-07 June 2010)

Crossed Oman coast near 21.50N between 0000 and 0200 UTC of 4 June

About 2 m at the time of landfall, issued 24 hrs in advance

2 m

CS, Bandu over AS(19-23 May2010)

Dissipated over Sea No storm surge warning No storm surge observed

SCS JAL over BoB (04-08 November 2010)

Crossed north Tamil Nadu and south Andhra Pradesh coast close to north of Chennai near 13.3/80.2 around 1600 UTC of 07 November as a Deep Depression

1-2m Low lying areas of Nellore, Prakasham dists of Andhra Pradesh and Tiruvallur, Chennai and Kanchipuram dists of Tamil Nadu, issued 48 hrs in advance. Later warning removed due to weakening of system

Negligible Inundation of low lying areas has been reported

CS KEILA over Arabian Sea (29 Oct-04 Nov, 2011)

Crossed Oman coast close to north of Salalah between 1600-1700 UTC of 02 Nov.

1m near landfall point, issued 12 hrs before landfall

No report was received from

OmanVSCS THANE over the BoB (25-31 Dec., 2011)

Crossed coast between Cuddalore and Puducherry within 0100 and 0200 UTC of 30 December, 2011

1-1.5m Puducherry, Tiruvallur, Villupuram, Chennai and Kanchipuram dists of north TN issued 48 hrs before landfall.

1m, Cuddalore, Puducherry and Villuparam districts

CS Murjan over Arabian Sea (23-26 Oct., 2012)

Crossed Somalia coast near 9.50N around 1200 UTC of 25th October

Not issued- No report received from

Somalia-CS Nilam over BoB (28 Oct.-01 Nov., 2012)

Crossed north TN coast near Mahabalipuram, between 1600-1700 hrs IST of 31st Oct

1-1.5 m over low lying areas of Chennai, Kanchipuram,

Tiruvallur and Nellore districts,24 hrs before landfall

1.3 m reported near Chennai

coast

Forecast Verification in IMD

• Lack of observational data over the oceanic region leading to

uncertainty in location of the system. The mean best track error may

be considered as 30 km.

• In the absence of the observations over the north Indian Ocean, the

best track of the cyclone is mostly estimated with the satellite

imagery interpretation with the help of Dvorak’s technique.

• However, this technique, which has been developed for north

Atlantic Ocean basin needs to be validated for north Indian Ocean.

Further automated Dvorak’s technique has to be

validated/developed for north Indian Ocean to minimize the human

error.

Limitations :Limitations : Intensity and track estimationIntensity and track estimation

Limitations : Track forecast error (km)

Limitations : Mean landfall point forecast error (km)

Mean landfall time forecast error (hr)

Average (2008-12)12 hr- 42 km24 hr- 91 km, 48 hr- 96 km 72 hr- 135 km

Average (2008-12)12 hr- 2.5 hrs24 hr- 5.5 hrs48 hr- 7.3 hrs 72 hr- 1.1 hrs

Prediction of total water envelop, taking into consideration the following:

•Storm surge

•Astronomical tide

•Wind wave and wave set up

•River discharge in the sea, and

•Rainfall distribution.

Parameters to be predicted:

•Height of TWLE

•Coastal inundation modeling

Prediction of above parameters should be attempted so that forecasting

is introduced in IMD

Operational requirements and Future Plan

Data on oceanography are concerned with:

(a) Bathymetry

(b) Astronomical tides, and

(c) Inshore currents in closed regions.

Accurate bathymetry maps are needed for improved surge

prediction. Better coastline representation is also needed.

The main hydrological information needed is:

(i) River discharge in the sea, and

(ii) Rainfall distribution.

LimitationsOceanographic and hydrological data

Schematic diagram showing various steps in volved in coastal inundation

modeling (WMO, 2013)

• TWLE and Coastal inundation modeling and hydrological modeling

will be taken up in a project mode in 2013/2014

Operational requirements and Future Plan

Thank youThank you