Intensification, Dissipation and GIS Tracking

How a tropical cyclone gains strength

A tropical cyclone is a rotating storm organised around a low-pressure centre. Its strength depends on a continuing supply of heat and moisture from the ocean. Intensification means that the storm becomes stronger, with increasing wind speeds.

Warm seas supply water vapour through evaporation. This warm, moist air rises within the storm, cools and condenses into cloud droplets. Condensation releases latent heat into the surrounding air. That heating encourages further rising air, helping to maintain the low-pressure centre and draw more air into the storm. This strengthens its circulation.

Sea temperatures of roughly 27°C or above provide favourable conditions. Warmer water can supply more heat and moisture, so a cyclone that remains over warm water has an opportunity to intensify. However, warm water alone does not guarantee that it will become stronger: atmospheric conditions also matter.

Why some storms intensify more than others

High humidity provides plenty of moisture for cloud formation and the release of latent heat. A storm with a strong supply of warm, moist air can therefore continue gaining energy.

Wind shear is a change in wind speed or direction with height. Low wind shear allows the storm’s rising air and rotating circulation to remain organised. Strong wind shear can displace the upper part of the storm from its lower-level circulation, disrupting the system. Two cyclones travelling over similarly warm seas may therefore develop differently if one encounters stronger wind shear.

Intensification is best understood as the combination of a good energy supply and an organised storm structure, rather than as the result of sea temperature alone.

How tropical cyclones dissipate

Dissipation is the weakening and eventual breakdown of the storm. It occurs when conditions stop supporting its energy supply or organised circulation.

When a cyclone moves over land, it loses direct access to the warm ocean water that supplied heat and moisture. Less moisture enters the storm, so less latent heat is released through condensation and the circulation weakens. Mountainous terrain can disrupt a cyclone particularly quickly.

Moving over cooler water also reduces the supply of heat and moisture. The storm can no longer sustain the same intensity. This helps explain why a cyclone’s strength may change as it follows its track across the ocean.

Encountering strong wind shear can break up the organised circulation, even while the cyclone is still over the sea. Dissipation is therefore not restricted to landfall.

Weakening is not always permanent. If a cyclone returns to sufficiently warm water and atmospheric conditions are favourable, it can regain its energy supply and re-intensify. A weakening cyclone can also still produce dangerous weather; dissipation does not mean that all hazards immediately disappear.

Tracking a cyclone with GIS

A geographical information system (GIS) links information to locations on a digital map. For cyclone tracking, points represent the storm centre at different times. Reading these points in chronological order reveals its track: where it travelled, its direction and whether its path changed.

Start with a basemap showing coastlines and an observed cyclone-track layer. Check the layer’s description, update time and legend, then select one cyclone. Use its point information or attribute table to compare positions and timestamps. Latitude tells you how far north or south a position lies; longitude tells you how far east or west it lies.

The following is a fictional teaching dataset, not a record of a real cyclone:

From 00:00 to 06:00, the storm moves northwards and eastwards: its northern latitude increases, while its western longitude moves closer to 0°. It continues towards the north-east over the next six hours, but the coordinate changes show that its track becomes more northward. This is a description of movement, not evidence that the storm is intensifying.

On an authentic GIS map, apply the same method to recorded positions. Use the map’s measurement tool to compare distances travelled during equal time intervals. A greater distance in the same time indicates faster movement of the storm centre. To assess intensification, you would also need intensity information, such as recorded wind speeds; the track alone is insufficient.

Separating observations from forecasts

Cyclone GIS layers may show both observed and forecast tracks. In Esri’s Active Hurricanes, Cyclones, and Typhoons layers, orange points represent the observed track, black points and text represent the forecast track, and a grey area shows the possible margin of error in the forecast. These colours are specific to that layer: always check the legend rather than assuming every map uses them.

Observed points show where the cyclone has already been recorded. Forecast points show where it is expected to go, not where it has definitely travelled. Compare the forecast with the coastline to identify places near its possible future path, while recognising the uncertainty shown around it.

Real-time layers update, so the map may change between visits and there may be no active cyclone to inspect. The fictional example demonstrates how to read a track, but only authentic, dated observations can establish the movement of a real storm.

Intensification

• Warm seas, roughly 27°C or above, supply heat and moisture.
• Rising moist air condenses → latent heat is released → rising air and circulation are strengthened.
• High humidity supplies moisture; low wind shear keeps the storm organised.

Dissipation

• Land: loss of the warm-ocean energy supply; mountains can disrupt the storm quickly.
• Cooler water: reduced heat and moisture supply.
• Strong wind shear: disruption of the organised circulation.
• Returning to warm water can allow re-intensification if atmospheric conditions are favourable.

GIS tracking

• Check the legend, timestamps and update time; select one cyclone.
• Compare successive recorded positions to identify direction and changes in its track.
• Compare distances over equal time intervals to assess movement speed.
• Track movement does not establish wind strength or intensification.
• Distinguish observed tracks from forecast tracks and their uncertainty.