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FAQ: Tropical Cyclone Forecasting

What regions around the globe have tropical cyclones and who is responsible for forecasting there?

Contributed by Chris Landsea

  1. There are seven tropical cyclone "basins" where storms occur on a regular basis:
  2. Atlantic basin (including the North Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea)
  3. Northeast Pacific basin (from Mexico to about the dateline)
  4. Northwest Pacific basin (from the dateline to Asia including the South China Sea)
  5. North Indian basin (including the Bay of Bengal and the Arabian Sea)
  6. Southwest Indian basin (from Africa to about 100E)
  7. Southeast Indian/Australian basin (100E to 142E)
  8. Australian/Southwest Pacific basin (142E to about 120W)

The National Hurricane Center in Miami, Florida, USA has responsibilities for monitoring and forecasting tropical cyclones in the Atlantic and Northeast Pacific basin east of 140W. The Central Pacific Hurricane Center in Honolulu has responsibilities for the remainder of the Northeast Pacific basin to the International Dateline. The Northwest Pacific basin is shared in forecasting duties by China, Thailand, Korea, Japan, the Philippines, and Hong Kong. The North Indian basin tropical cyclones are forecasted by India, Thailand, Pakistan, Bangladesh, Burma, and Sri Lanka. Reunion Island, Madagascar, Mozambique, Mauritius, and Kenya provide forecasts for the Southwest Indian basin. Australia and Indonesia forecast tropical cyclone activity in the Southeast Indian/Australian basin. Lastly, for the Australian/Southwest Pacific basin Australia, Papua New Guinea, Fiji, and New Zealand forecast tropical cyclones. Note also that the US Joint Typhoon Warning Center (JTWC) issues warnings for tropical cyclones in the Northwest Pacific, the North Indian, the Southwest Indian, the Southeast Indian/Australian, and the Australian/Southwest Pacific basins, though they are not specifically tasked to do so by the WMO. The US Naval Pacific Meteorology and Oceanography Center in Pearl Harbor, Hawaii does the same for the Pacific Ocean east of 180E. (Neumann 1993)

Note that on rare occasions, tropical cyclones (or storms that appear to be similar in structure to tropical cyclones) can develop in the Mediterranean Sea. These have been noted to occur in September 1947, September 1969, January 1982, September 1983, and, most recently, during 13 to 17 January, 1995. Some study of these storms has been reported on by Mayengon (1984) and Ernest and Matson (1983), though it has not been demonstrated fully that these storms are the same as those found over tropical waters. It may be that these Mediterranean tropical cyclones are more similar in nature to polar lows.

The recent hurricane that formed in the South Atlantic was handled by the Brazilian weather service. Since tropical cyclones are so rare in this region, the WMO has not designated a forecast center with responsibility for there.

The following are the addresses of tropical cyclone centers listed above that are responsible for issuing advisories and/or warnings on tropical cyclones (thanks to Jack Beven for these):

World Meteorological Organization

WWW: http://www.wmo.int/pages/index_en.html

National Hurricane Center

Mail: 11691 SW 17th St. Miami, FL 33165-2149 USA

WWW: http://www.nhc.noaa.gov/index.html

Email : Frank Lepore Public Affairs Officer

Central Pacific Hurricane Center

Mail: National Weather Service Forecast Office Central Pacific Hurricane Center 2525 Correa Rd. Suite 250 Honolulu, HI 96822 USA

WWW: http://www.prh.noaa.gov/cphc

Naval Pacific Meteorological and Oceanographic Center

Mail: NPMOC/AJTWC Box 113 Pearl Harbor, HI 96860 USA

WWW: http://metocph.nmci.navy.mil/

Joint Typhoon Warning Center

Mail: NAVPACMETOCCEN/JTWC 425 Luapele Rd. Pearl Harbor, HI 96860 USA

Regional Specialized Meteorological Center Tokyo, Japan - Typhoon Center

Mail: Japanese Meteorological Agency 1-3-4 Ote-machi, Chiyoda-ku Tokyo Japan

WWW: http://www.jma.go.jp/jma/jma-eng/jma-center/rsmc-hp-pub-eg/RSMC_HP.htm

Hong Kong Observatory

Mail: 134A Nathan Road Kowloon Hong Kong

WWW: http://www.info.gov.hk/hko/index.htm

Bangkok Tropical Cyclone Warning Center - Thailand

Mail: Director Meteorological Department 4353 Sukumvit Rd. Bangkok 10260 Thailand

Fiji Tropical Cyclone Warning Center

Mail: Director Fiji Meteorological Services Private Mail Bag Nadi Airport Fiji

New Zealand Meteorological Service

Mail: Director Met Service PO Box 722 Wellington New Zealand

WWW: http://www.metservice.co.nz/index.asp

Port Moresby Tropical Cyclone Warning Center

Mail: Director National Weather Service PO Box 1240 Boroko, NCD Paupa New Guinea

Brisbane Tropical Cyclone Warning Center

Mail: Regional Director Bureau of Meteorology GPO Box 413 Brisbane 4001 Australia

WWW: http://www.bom.gov.au/weather/qld

Darwin Tropical Cyclone Warning Center

Mail: Regional Director Bureau of Meteorology Northern Territory Regional Office PO Box 40050, CASUARINA, N.T. 0801 Australia

WWW: http://www.bom.gov.au/weather/nt

Perth Tropical Cyclone Warning Center

Mail: Regional Director Bureau of Meteorology GPO Box 1370 West Perth,WA 6872 Australia

WWW: http://www.bom.gov.au/weather/wa

Jakarta, Indonesia

Mail: Director Analysis and Processing Centre Jalan Arief Rakhman Hakim 3 Jakarta Indonesia

Regional Tropical Cyclone Advisory Centre - Reunion

Mail: Director of Meteorological Services PO Box 4 97490 Sainte Clotilde Reunion

WWW: http://www.meteo.fr (Le temps/ Outre-mer/ La Reunion)

Sub-Regional Tropical Cyclone Warning Center - Mauritius

Mail: Director of Meteorological Service Vacoas Mauritius

Sub-Regional Tropical Cyclone Warning Center - Madagascar

Mail: Director of Meteorological Service PO Box 1254 Antananarivo 101 Madagascar

Nairobi, Kenya

Mail: Director of Meteorological Services PO Box 30259 Nairobi Kenya

Maputo, Mozambique

Mail: Director of Meteorology PO Box 256 Maputo Mozambique



The following cities are also mentioned as tropical cyclone warning centers, though I don't have the addresses for them.

Philippines: Manila

China: Beijing Dalian Shanghai Guangzhou

Korea: Seoul

Vietnam: Hanoi

India: New Delhi Calcutta Bombay

Bangladesh: Dhaka

Burma: Rangoon

Sri Lanka: Colombo

Maldive Islands: Male

 

What are those track and intensity models that the Atlantic forecasters are talking about in the Inter-Governmental messages?

Contributed by Sim Aberson

A variety of hurricane track forecast models are run operationally for the Atlantic hurricane basin:

  1. The basic model that is used as a "no-skill" forecast to compare other models against is CLIPER (CLImatology and PERsistence), which is a multiple regression statistical model that best utilizes the persistence of the current motion and also incorporates climatological track information (Aberson 1998). Surprisingly, CLIPER was difficult to beat with numerical model forecasts until the 1980s.
  2. A statistical-dynamical model, NHC90 (McAdie 1991), uses geopotential height predictors from the Aviation model to produce a track forecast four times per day. The primary synoptic time NHC90 forecasts (00 and 12 UTC) are based upon 12 h old Aviation runs. A special version of NHC90, NHC90-LATE, is run at primary synoptic times with the current Aviation run, and is available a number of hours after NHC90. Both versions of NHC90 have been run operationally since 1990. An update to this model, NHC98, was implemented in 1998.
  3. The Beta and Advection Model (BAM), follows a trajectory in the pressure-weighted vertically-averaged horizontal wind from the Aviation model beginning at the current storm location, with a correction that accounts for the beta effect (Marks 1992). Three versions of this model, one with a shallow-layer (BAMS), one with a medium-layer (BAMM), and one with a deep-layer (BAMD), are run. BAMS runs using the 850-700 mb layer,BAMM with the 850-400 mb layer, and BAMD with the 850-200 mb layer. The deep-layer version was run operationally for primary synoptic times in 1989; all three versions have been run four times per day since 1990.
  4. A nested barotropic hurricane track forecast model (VICBAR) has been run four times daily since 1989. The primary synoptic time runs are run from current NCEP analyses, the off-time runs are run from six hour old data (Aberson and DeMaria 1994). Another barotropic model, LBAR, for Limited-Area Barotropic Model, is also being run operationally every 6 hours which performs slightly worse than VICBAR, but is available earlier for use by the NHC forecasters.
  5. The NCEP Aviation and MRF models (Lord 1993) has been used for track forecasting since the 1992 hurricane season. These are global models.
  6. A triply-nested movable mesh primitive equation model developed at the Geophysical Fluid Dynamics Laboratory (Bender et al 1993), known as the GFDL model, has provided forecasts since the 1992 hurricane season.
  7. The United Kingdom Meterological Office's global model (UKMET) is utilized for forecasting the track of tropical cyclones around the world (Radford 1994). The National Hurricane Center starting receiving these operationally during 1996.
  8. The United States Navy Operational Global Atmospheric Prediction Systems (NOGAPS) is also a global numerical model that shows skill in forecasting tropical cyclone track (Fiorino et al. 1993). This model was also first received operationally at the National Hurricane Center during 1996.
Despite the variety of hurricane track forecast models, there are only a few models that forecast intensity change for the Atlantic basin:
  1. Similar to the CLIPER track model, the SHIFOR (Statistical Hurricane Intensity Forecast model) is used as a "no-skill" intensity change forecast. It is a multiple regression statistical model that best utilizes the persistence of the intensity trends and also incorporates climatological intensity change information (Jarvinen and Neumann 1979). SHIFOR has been difficult to exceed until recent years.
  2. A statistical-synoptic model, SHIPS (Statistical Hurricane Intensity Prediction Scheme ), has been available to the National Hurricane Center since the mid-1990s (DeMaria and Kaplan 1994). It takes current and forecasted information on the synoptic scale on the sea surface temperatures, vertical shear, moist stability, etc. with an optimal combination of the trends in the cyclone intensity.
  3. The GFDL model, described above in the track forecasting models, also issues forecasts of intensity change for the National Hurricane Center.
  4. A new statistical scheme for estimating the probability of rapid intensification has been developed (Kaplan and DeMaria 1999) and is now being used operationally. The RI scheme employs synoptic and persistence information from the SHIPS model to estimate the probability of rapid intensification (24 h increase in maximum wind of 35 mph or greater) every 6 hours.



What are the various forecasts that are being issued for seasonal tropical cyclone activity around the world?

Contributed by Stan Goldenberg

There are a number of different seasonal forecasts currently being issued for various basins. Some of these are fairly new, while the oldest and most well known ( Prof. Bill Gray's forecast from CSU) has been issued for almost two decades.


What is the official U.S. Government (NOAA) seasonal hurricane outlook for the the Atlantic basin for this year and what are the predictive factors?

Contributed by Stan Goldenberg

Click here to go to the NOAA outlook and a listing of the predictive factors used.



How has the official U.S. Government (NOAA) seasonal hurricane outlook done in previous years?

Contributed by Stan Goldenberg

The NOAA Seasonal Outlook for Atlantic basin hurricane activity does not predict numbers of tropical storms, hurricanes and major hurricanes directly. Rather, the scheme is set up to forecast a range of expected values for the ACE index (Accumulated Cyclone Energy), a measure of overall activity. The ranges predicted for numbers of systems are obtained by looking at the years in the historical record which had observed values for ACE in the predicted range for the current year. Note that although the range for ACE might verify correctly for a given year (as it has so far for every year since the forecast began in 1998 -- see below), it is rare that the ranges for all three numbers (tropical storms, hurricanes and major hurricanes) will be correct. However, if ACE is correct, then usually at least two of the predicted ranges for numbers are correct as well. (Click here to see a chart of the observed values for ACE since 1950.)



How accurate are the forecasts from the National Hurricane Center?

Contributed by Chris Landsea and Miles Lawrence

The National Hurricane Center (NHC) issues an official forecast, every six hours, of the center position, maximum one-minute surface (10 meter [33 ft] elevation) wind speed (intensity), and radii of the 34 knot (39 mph,63 kph), 50 knot (58 mph,92 kph), and 64 knot (74 mph,117 kph) wind speeds in four quadrants (northeast, southeast, southwest, and northwest) surrounding the cyclone. The NHC has been issuing predictions for the forecast periods of 12, 24, 36, 48, and 72 hours since 1964. Forecasts for 12 and 24 hours were first issued in 1954. In 2003, the forecasts were extended and now include 96 and 120 hours. All official forecast are verified by comparison with the "best track", a set of six-hour center positions and maximum wind speed values, that represents the official NHC estimate of the location and intensity of a tropical cyclone. A best track is prepared for every tropical cyclone, after the fact, using all available data.

NHC's official track errors have averaged in the last few years about 85 nmi (100 st. miles,160 km) at 24 hr, 140 nmi (160 st. miles,260 km) at 48 hr and 200 nmi (230 st. miles,370 km) at 72 hr. One can see that NHC has even done better than these numbers during 2003. Forecasts are now also issued at 4 and 5 days lead time and these are likely to have an average error of about 250 nmi (290 st. miles,460 km) and 300 nmi (350 st. miles, 550 km), respectively. These are average errors so, of course, individual predictions may be substantially better or worse. It is to the National Hurricane Center's credit (and NOAA in general) that these predictions have gotten so much better in the last few decades, due to a combination of more accurate numerical models, more observations over the open ocean, and a better understanding of the physics of hurricane movement. Today a 3 day forecast is as accurate as those issued for a 2 day prediction in the late 1980s.

NHC's wind intensity errors have averaged recently about 9 kt (10 mph,17 kph) at a 24 hr forecast, 15 kt (17 mph,28 kph) at a 48 hr forecast, and 19 kt (22 mph,35 kph) at a 72 hr forecast. The 4 and 5 day predictions should average about 21 kt (24 mph,39 kph) and 22 kt (25 mph,41 kph). (One comparison of the ability of the long-range forecasts is to consider that a simple prediction of a constant value of 60 kt (70 mph,110 kph) gives an error of about 23 kt (26 mph,43 kph), so forecasts with errors close to this value have little to no skill.) One does see that the intensity forecasts have improved somewhat at 1 and 2 day predictions - 48 hr forecasts today have errors that are 20% smaller than they were in the mid-1970s.

However, the improvements are much slower than in the track predictions and the 3 day forecasts of intensity have not gotten substantially better at all. Much work still remains to better understand and predict wind intensity changes in tropical storms and hurricanes.

Tropical cyclone size (that is, the radius of high winds) has been been forecasted by NHC for several years, though the first quantitative verifications have been provided just recently. These suggest that the errors in predicting the radius of gale force winds (34 kt,39 mph,63 kph) averages about 20 nmi (25 st. miles,35 km) at a 24 hr forecast, about 25 nmi (30 st. miles,45 km) at a 48 hr forecast, and about 30 nmi (35 st. miles,55 km) at a 72 hr forecast.

Last updated August 13, 2004



How is storm surge forecast?

Contributed by the National Hurricane Center

Storm surge, the abnormal rise of ocean water on land due primarily to strong onshore winds, is primarily forecast with the SLOSH computer model. SLOSH (Sea, Lake and Overland Surges from Hurricanes) is run by the National Hurricane Center (NHC) to estimate storm surge heights and winds resulting from historical, hypothetical, or predicted hurricanes by taking into account five factors: the winds, the central pressure, the size, the forward speed and the track direction of the hurricane.

The calculations are applied to a specific locale's shoreline, incorporating the unique bay and river configurations, water depths, bridges, roads and other physical features. If the model is being used to estimate storm surge from a predicted hurricane (as opposed to a hypothetical one), forecast data must be put in the model every 6 hours over a 72-hour period and updated as new forecasts become available.

The SLOSH model is generally accurate within plus or minus 20 percent. For example, if the model calculates a peak 10 foot (3.0 m) storm surge for the event, you can expect the observed peak to range from 8 to 12 feet (2.4 to 3.6 m). The model accounts for astronomical tides (which can add significantly to the water height) by specifying an initial tide level, but does not include rainfall amounts, riverflow, or wind-driven waves. However, this information is combined with the model results in the final analysis of at-risk-areas.

The point of a hurricane's landfall is crucial to determining which areas will be inundated by the storm surge. Where the hurricane forecast track is inaccurate, SLOSH model results will be inaccurate. The SLOSH model, therefore, is best used for defining the potential maximum surge for a location.


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Source: "FAQ Tropical Cyclone Forecasting." NOAA. 1 June 2007. Date Accessed: 30 September 2008.

Page Last Updated: 10/17/08 15:29

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