Proposed Amendments to Chapter 15, Article X: Wetland Conservation Areas
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1. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Tropical Cyclones
Characteristics and Forecasting
Horace H. P. Burton and Selvin DeC. Burton
Caribbean Institute for Meteorology and Hydrology
2. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Outline
โข Introduction
* Definitions
* Characteristics
โข Forecast Methods
โข Forecast errors
โข Probability forecasts
3. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Definitions
โข Tropical cyclone
An area of low pressure which develops over
tropical or subtropical waters
โข Tropical depression
A weak tropical cyclone in which the maximum
surface wind is 38 mph (62 km/h or 33 kt) or less
4. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Definitions
โข Tropical storm
A tropical cyclone in which the maximum surface
wind ranges from 39 to 73 mph (63 to 118 km/h or
34 to 64 kt)
โข Hurricane
A tropical cyclone with highest sustained winds 74
mph (119 km/h or 65 kt) or more
6. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Tropical Cyclone Characteristics
โข Season - June to November
โข Average - 9 tropical storms
- 6 hurricanes
โข Most active months - August and September
โข Movement - west or west northwest
- recurve to east generally in western
and northwestern Atlantic
7. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Tropical Cyclone Characteristics
โข Size - 300 to 1500 km in diameter
โข Horizontal structure
* Eye - 20 km
* Eyewall - 30 to 50 km
* Spiral bands
8. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Tropical Cyclone Characteristics
โข Hurricane force winds generally extend out about
100 km (60 miles) from the centre
โข Storm force winds may extend out as much as 500
km (300 miles)
โข Maximum wind speeds between 12 and 50 km
from centre
9. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Tropical Cyclone Forecasting
โข Early and precise warnings (forecasts) do not
necessarily remove the risk of damage or loss or
life, but the effects may be significantly reduced
โข Current inaccuracies in forecast dictate over
warning
โข False warnings can produce an attitude of
scepticism
10. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Forecasting Methods
โข Forecasting methods have evolve to become more
complex
* Pre 1960 - simple subjective methods
โข cloud types and motion, swells, pressure
* Post 1960 - more sophisticated objective
methods
โข complex statistical techniques and computer models
11. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Forecasting Methods
โข A tropical cyclone forecast involves the prediction
of several interrelated features, including
* The track, winds, rainfall, storm surge, areas
threatened
โข NHC normally issues a forecast every 6 hours for
period extending out to 72 hours
โข Official forecast is based on the guidance obtained
from a variety of subjective and objective models
12. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Forecast Errors
โข Forecast errors arise from
* A lack of a full understanding of the formation
and growth of tropical cyclones
* The limitations of the forecasting techniques
โข Users of forecasts must be aware of the limitations
of information in advisories
13. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Forecast Errors - characteristics
โข Still substantially large although showing a slow
and steady decrease
โข Increase remarkably with increasing time
โข Are approximately 30 % of the cyclone movement
over the same time
โข Large year-to-year variations
14. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Official Forecast Errors for Atlantic
Forecast Interval (hr)
0 12 24 36 48 72
Track in km (1986-1995) 26 91 173 252 335 506
Intensity in kt (1990-1995) 3 7 10 13 16 19
15. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Initial forecast errors
โข Average official initial forecast errors
* 26 km for position
* 3 kt for intensity
โข Range of initial forecast errors
* 10 km for good eye to more 180 km for poorly
defined centre
* as much as 30 kt for intensity
16. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Strike probability forecasts
โข One method use to objectively define uncertainty
inherent in forecasts
โข Derived from knowledge of past cyclones and
forecast errors in the region of interest
โข Provide valuable early guidance in estimating the
risk of tropical cyclones affecting important or
vulnerable facilities
17. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Use of strike probability forecasts
โข To extend the usable length of forecasts
โข To provide a quantitative assessment of the threat
posed by a tropical cyclone
โข To compare the relative threat
โข To cause a consistent response
โข As a tool in risk analysis
18. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Probability ellipses - Georges 1998
19. Caribbean Disaster Mitigation Project
Caribbean Institute for Meteorology and Hydrology
Strike probability forecasts
โข Uncertainty increases as the forecast interval
increases
โข 72 hours probability less than that 12 hours
โข Maximum probability at 72 hours is about 10%
compared to about 70% at 12 hours
โข Longer lead-time actions must be based on
smaller probabilities
