How are hurricanes forecast?

Published: 26th August 2008
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Hurricane forecasting is heavily reliant on computer models. There are many different hurricane forecasts available which are built on different mathematical equations. Because of this, hurricane track and intensity forecasts will differ. One must know which of the hurricane forecast models is performing the best.

Hurricane forecasts are also dependent on available observational data. Unfortunately, over the tropics, data is sparse. Sometimes a hurricane or tropical storm will weaken or strengthen when not forecasted to do so. This can sometimes be attributed to lack of data available to the forecast models to come up with a proper solution. The forecasts can be only as accurate as the data will allow.

It is also not wise to jump on a forecast model that deviates significantly from previous forecasts. Watch for trends in the forecast track. Also, do not focus on the forecast track many days in the future. The farther out in time, the greater the average forecast error. Any correct forecast based on a track one week or more in the future would require a great deal of luck.

Hurricane intensity forecasts are less understood than hurricane track forecasts. Sometimes hurricanes deepen or strengthen very rapidly. This process is not well understood yet, but likely occurs when a combination of synoptic and meso-scale features both favor an increase in strength. This rapid deepening usually occurs in the deep tropics where the wind shear is low and outflow high in the atmosphere is very strong.

In a similar fashion, a tropical cyclone can weaken very rapidly. There are two main causes for this. The first one is wind shear. When a tropical storm or hurricane approaches strong upper air winds, it can tear apart the circulation. The low level winds in the tropics are generally from the east. At higher altitudes, especially at higher latitudes, winds in the upper troposphere blow generally from the west. This is the shearing action that can weaken a tropical cyclone rapidly. Another mechanism that causes tropical cyclones to weaken is dry air. Usually the air is moist enough at the low levels in the deep tropics to allow tropical cyclone development. Sometimes dry air in the mid levels of the atmosphere is ingested into the circulation which disrupts the ability of the tropical storm or hurricane to produce the energy that it feeds on - moist unstable air.

Good hurricane forecasters know how to interpret all of the tools at their disposal. This includes visible, infer red, and water vapor satellite imagery. It is essential to be able to correctly analyze wind flow patterns at low, middle, and high levels of the troposphere. Satellite derived winds are also very useful. Buoy data, ship reports, radar imagery and Hurricane Hunter information are also extremely important to interpret correctly.

In recent years the media has obtained hurricane forecast information without forecasters trained in proper interpretation. This has led to the improper dissemination of information to the public. The most important aspect in hurricane forecasting is experience. Nothing can replace lessons learned after many years studying the eccentricities of hurricanes.

In summary, hurricane forecasters should be experienced and know how to correctly use the tools available to them. Forecasting is also an art. A good hurricane forecaster must know how to assimilate the intangibles.

Rich Johnson - Expert Hurricane Forecasts | Travel Resources

Rich is a Certified Broadcast Meteorologist with 25 years of weather forecasting and television experience. His expertise is in tropical meteorology forecasting hurricanes. His website is dedicated to helping travelers cope with tropical weather.

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