Subject: F1) What regions around the globe have tropical cyclones and who is responsible for forecasting there? Contributed by Chris Landsea There are seven tropical cyclone "basins" where storms occur on a regular basis: Atlantic basin (including the North Atlantic Ocean, the Gulf of Mexico, and the Caribbean Sea) Northeast Pacific basin (from Mexico to about the dateline) Northwest Pacific basin (from the dateline to Asia including the South China Sea) North Indian basin (including the Bay of Bengal and the Arabian Sea) Southwest Indian basin (from Africa to about 100E) Southeast Indian/Australian basin (100E to 142E) Australian/Southwest Pacific basin (142E to about 120W) The TPC 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.ch/web/www/TCP/rsmcs.html TPC Mail: 11691 SW 17th St. Miami, FL 33165-2149 USA WWW: http://www.nhc.noaa.gov/index.html 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 Joint Typhoon Warning Center Mail: NAVPACMETOCCEN/JTWC 425 Luapele Rd. Pearl Harbor, HI 96860 USA WWW: http://www.npmoc.navy.mil/ Regional Specialized Meteorological Center Tokyo, Japan - Typhoon Center Mail: Japanese Meteorological Agency 1-3-4 Ote-machi, Chiyoda-ku Tokyo Japan WWW: http://www.goin.nasda.go.jp/GOIN/JMA/ 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 Subject: F2) What are those track and intensity models that the Atlantic forecasters are talking about in the hurricane and tropical storm Discussions? Contributed by Sim Aberson and John Kaplan The major hurricane track forecast models run operationally for the Atlantic, Eastern Pacific, and Central Pacific hurricane basins are: - 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. - 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. - A barotropic hurricane track forecast model LBAR, for Limited-Area Barotropic Model, is being run operationally every 6 hours. - The NOAA Global Forecast System (GFS), formerly known as the Aviation and MRF models (Lord 1993) has been used for track forecasting since the 1992 hurricane season. An ensemble of lower-resolution runs is available four times daily. (See www.emc.ncep.noaa.gov/index.php?branch=GFS for Current information on the GFS) - 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. One version (GFDL) uses GFS fields for boundary conditions; a second version (GFDN) uses NAVGEM fields for boundary conditions. (See www.gfdl.noaa.gov/operational-hurricane-forecasting for Current information on the GFDL model) - A doubly-nested movable mesh primitive equation non-hydrostatic model known as HWRF (for the Hurricane Weather Research and Forecast Model), has provided forecasts since 2006. It uses GFS fields for boundary conditions (Gopal et al 2012). (See www.emc.ncep.noaa.gov/index.php?branch=HWRF for Current information on HWRF) - The United Kingdom Meterological Office's global Unified model is utilized for forecasting the tracks of tropical cyclones around the world (Radford 1994) . NHC starting receiving these operationally in 1996. (See www.metoffice.gov.uk/research/modelling-systems/unified-model for Current information on the Unified Model) - The United States Navy Global Environmental Model (NAVGEM) 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. An ensemble of lower-resolution runs is available twice daily. (See www.nrlmry.navy.mil/metoc/nogaps/nogaps_char.html for current information on NAVGEM) - The Canadian Meteorological Center's Global Environmental Multi-scale Model (GEM) provides forecasts twice per day. An ensemble of lower-resolution runs is available twice daily. (See collaboration.cmc.ec.gc.ca/science/rpn/gef_html_public/index.html for current information on GEM) - The European Centre for Medium-Range Weather Forecasts's Integrated Forecast System (IFS) provides forecasts twice per day. It has proven to be the best model for track forecasting, and is the highest resolution global model available. An ensemble of lower-resolution runs is available twice daily. (See www.ecmwf.int/products/data/operational_system/ for Current information on the IFS) - The Japanese Meteorological Agency's Global Spectral Model (GSM) provides forecasts, both in high-resolution deterministic runs and lower-resolution ensemble runs. (See www.jma.go.jp/jma/en/Activities/nwp.html for current information on the GSM) The full list of models used in the Atlantic and Eastern and Central Pacific is available here ftp.nhc.noaa.gov/atcf/docs/nhc_techlist.dat Various types of consensus models (ensemble means) are available from these models. Despite the variety of hurricane track forecast models, there are only a few models that provide operational intensity change forecasts for the Atlantic and Eastern and Central Pacific basins: - 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. - A statistical-synoptic model, SHIPS (Statistical Hurricane Intensity Prediction Scheme), has been available 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. - The Logistic Growth Equation Model (LGEM) uses the same inputs as the SHIPS model but uses a dynamical scheme. The intensity is determined by a logistic growth equation contrained by the maximum potential intensity as derived from the sea surface temperature. LGEM differs from SHIPS in that it accounts for changes in environmental conditions rather than using values averaged over the forecast period. - The GFDL and HWRF models, described above in the track forecasting models, also issue forecasts of intensity change. - A statistical scheme for estimating the probability of rapid intensification has been developed (Kaplan et al 2010) 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. For information on the performance of these models is available after each season see www.nhc.noaa.gov/verification/ Last Updated : May 23, 2013 Subject: F3) 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. North Atlantic Basin: Prof. Bill Gray, Department of Atmospheric Science, Colorado State University CPC/HRD/NHC Team, National Oceanic and Atmospheric Administration Mark Saunders, Tropical Storm Risk, Department of Space and Climate Physics, University College London Florida State University NW Pacific: Mark Saunders, Tropical Storm Risk, Department of Space and Climate Physics, University College London Prof. Johnny C. L. Chan, Laboratory for Atmospheric Research, Dept. of Physics & Mat. Sci., City University of Hong Kong Australian Basin: Mark Saunders, Tropical Storm Risk, Department of Space and Climate Physics, University College London South China Sea: Prof. Johnny C. L. Chan, Laboratory for Atmospheric Research, Dept. of Physics & Mat. Sci., City University of Hong Kong Subject: F4) 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 Go here to go to the NOAA outlook and a listing of the predictive factors used. http://www.cpc.ncep.noaa.gov/products/outlooks/hurricane.shtml Subject: F5) 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. Verification for the NOAA May Seasonal Outlook for the North Atlantic basin hurricane activity from 1999 - 2003 http://www.aoml.noaa.gov/hrd/tcfaq/noaamay04.JPG Verification for the NOAA August Seasonal Outlook for the North Atlantic basin hurricane activity from 1998 - 2003 http://www.aoml.noaa.gov/hrd/tcfaq/noaaaug04.JPG Last updated August 13, 2004 Subject: F6) How accurate are the forecasts from the National Hurricane Center? Contributed by Chris Landsea and Miles Lawrence The National Hurricane Center (TPC) 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 combintation 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 Subject: F7) How is storm surge forecast at NHC? Contributed by the NHC Storm Surge Unit The Sea, Lake, and Overland Surges from Hurricanes (SLOSH) model is the computer model utilized by the National Oceanic and Atmospheric Administration (NOAA) for coastal inundation risk assessment and the operational prediction of storm surge. The eastern seaboard and Gulf Coast of the United States, Puerto Rico, the Bahamas, the Virgin Islands, and Hawai'i, are subdivided into 39 regions or "basins." These areas represent sections of the coastline that are centered upon particularly susceptible features: inlets, large coastal centers of population, low-lying topography, and ports. The SLOSH model computes the maximum potential impact of the storm in these "computational domains" based on storm intensity, track, and estimates of storm size provided by hurricane specialists at NHC. Currently, SLOSH basins are being updated at an averate rate of 6 basins per year. SLOSH basin updates are ultimately governed by the Interagency Coordinating Committee on Hurricanes (ICCOH). ICCOH manages hazard and post-storm analysis for the Hurricane Evacuation Studies under FEMA's Hurricane Program. Updates are driven by a number of different factors such as: changes to a basin's topography/bathymetry due to a hurricane event, degree of vulnerability to storm surge, availability of new data, changes to the coast, and addition of engineered flood protection devices (e.g. levees). Sometimes these updates include higher grid size resolution to improve surge representation, increasing area covered by hypothetical tracks for improved accuracy, conversion to updated vertical reference datums, and including the latest topography or bathymetric data for better representation of barrier, gaps, passes, and other local features. The SLOSH model can generate sevel different products : - Deterministic runs This is an operational product based on the official NHC track and intensity forecast of a tropical cyclone. Operational SLOSH runs are generated whenever a hurricane warning is issued, approximately 36 hours prior to arrival of tropical storm winds. It is run every 6 hours coinciding with the full advisory package. This is a single run product which can result in uncertainty because it is STRONGLY dependent on the accuracy of the storm track and timing. This product is intended to provide valuable surge information in support of rescue and recovery efforts. - Probabilistic runs (P-surge) This is a graphical product using an ensemble of many SLOSH runs to create a Probabilistic Storm Surge (P-Surge) product. This is intended to be used operationally so it is based on NHC's official advisory. P-Surge uses SLOSH-based simulations which are based on statistics of past performance of the advisories. These different SLOSH simulations are based on the distribution of : - Cross-track error (impacts landfall location) - Along-track error (impacts forward speed and timing) - Intensity error (impacts pressure) - Size error (impacts size) P-Surge is available whenever a hurricane watch or warning is in effect. It is posted on the NHC webpage within approximately 30 minutes after the advisory release time. - Maximum Envelope of Water (MEOW) runs This is an ensemble product representing the maximum height of storm surge water in a given basin grid cell using hypothetical storms run with the same: - Category (intensity) - Forward speed - Storm trajectory - Initial tide level Internally a number of parallel SLOSH runs with same intensity, forward speed, storm trajectory, and initial tide level are performed for the basin. The only difference in runs is that each is conducted at some distance to the left or right of the main track (typically at the center of the grid). Each component run computes a storm surge value for each grid cell. For example, five parallel runs may yield storm surge values of 4.1, 7.1, 5.3, 6.3, and 3.8 feet. In this case, the MEOW for the cell is 7.1 ft. It is unknown (to the user) which track generated the MEOW for a particular cell, so it is entirely possible that the MEOW values for adjacent cells may have come from different runs. MEOWs are used to incorporate the uncertainties associated with a given forecast and help eliminate the possibility that a critical storm track will be missed in which extreme storm surge values are generated. MEOWs provide a worst case scenario for a particular category, forward speed, storm trajectory, and initial tide level incorporating uncertainty in forecast landfall location. The results are typically generated from several thousand SLOSH runs for each basin. Over 80 MEOWs have been generated for some basins. This product provides useful information aiding in hurricane evacuation planning. - Maximum of MEOW (MOM) runs This is an ensemble product of maximum storm surge heights for all hurricanes of a given category regardless of forward speed, storm trajectory, landfall location, etc.. MOMs are created internally by pooling all the MEOWs for a given basin, separated by category and tide level (zero/high), and selecting the MEOW with the greatest storm surge value for each basin grid cell regardless of the forward speed, storm trajectory, landfall location, etc. This procedure is done for each category of storm. Essentially, there is 1 MOM per storm category and tide level (zero/high). MOMs represent the worst case scenario for a given category of storm under "perfect" storm conditions. The MOMs provide useful information aiding in hurricane evacuation planning and are also used to develop the nation's evauation zones. Strengths and limitations of SLOSH The SLOSH model is computationally efficient resulting in fast computer runs. It is able to resolve flow through barriers, gaps, and passes and models deep passes between bodies of water. It also resolves inland inundation and the overtopping of barrier systems, levees, and roads. It can even resolve coastal reflections of surges such as coastally trapped Kelvin waves. However it does not model the impacts of waves on top of the surge, account for normal river flow or rain flooding, nor does it explicitly model the astromical tide (although operational runs can be run with different water level anomalies to model conditions at the onset of operational runs). Last updated May 14, 2010 Subject: F8) How is storm surge observed and measured? Contributed by the NHC Storm Surge Unit There are several methods used by NOAA, the United States Geological Survey (USGS), and the Federal Emergency Management Agency (FEMA) to measure storm surge. Each method has advantages and draw backs and post-storm analysis of storm surge requires resolving differences in what each measures to find the best approximation of the surge heights. - Tide Stations (NOAA) A network of 175 long-term, continuously operating water level stations located throughout the U.S. serving as the foundation for NOAA's tide prediction products. * Measures still water (e.g. no waves) * Traditionally the most reliable method * Limited, fixed stations - High Water Marks (USGS / FEMA) These are the lines left on trees and structures marking the highest (peak) elevation of the water surface from a flood event. They are created by foam, seeds, and other debris. Survey crews deploy after a storm, locate, and record reliable high water marks. GPS methods are used to determine the location of these marks, which are then mapped relative to a vertical reference datum. * Perishable * Traditionally best method for capturing highest surge level * Subjective and often includes impact of waves - Pressure Sensors (USGS) These are temporary water-level and barometric-pressure sensors which provide information about storm surge duration, times of surge arrival and retreat, and maximum depths. * Relatively new method * Mobile, deployed in advance of storms at expected location of highest surge * Can contain impact of waves Last updated May 14, 2010