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RAMMB: Regional and Mesoscale Meteorology Branch CIRA: Cooperative Institute for Research in the Atmosphere

Real-Time Tropical Cyclone Products - Description of Products

Overview

The purpose of this web site is to display in a real-time manner tropical cyclone products created and/or developed by NOAA/NESDIS/STAR/RAMMB and associated CIRA scientists over the last 20 years. While there is some overlap with other tropical cyclone web pages an effort has been made to show unique products not displayed elsewhere. To serve these data to the public the web page is also integrated to a database that can accommodate future product development. Because the site is a developing project, current products may be unavailable at earlier times.

Track Forecasts

Track forecasts are provided by three forecast centers via databases contained in the Automated Tropical cyclone Forecast (ATCF) system (Sampson and Schrader 2000). Forecasts for the North Atlantic and eastern North Pacific are provided by the National Hurricane Center (NHC), which is located in Miami, FL. Forecasts for the Central North Pacific (140W to the Dateline) are provided by the Central Pacific Hurricane Center (CPHC ) located in Honolulu, HI. Both NHC and CPHC are part of the NOAA National Weather Service. Forecast information for the western North Pacific, North Indian Ocean, and the Southern Hemisphere are provided by the Joint Typhoon Warning Center (JTWC ) located at Pearl Harbor, HI. The JTWC is part a US Department of Defense and provides tactical tropical cyclone forecasts for the US armed forces. Note that forecasts are 6-hourly in all basins except the Southern Hemisphere (12-hourly) and that forecasts are made through 5 days (120h) except in the North Indian Ocean (through 72h) and the Southern Hemisphere (48h).

Sampson, C. R., and A. J. Schrader, 2000: The Automated Tropical Cyclone Forecasting System (Version 3.2). Bull. Amer. Meteor. Soc., 81, 1131-1240.

Track History

Track history for each storm is created from the operational warnings that are issued every six hours by NHC, CPHC , and JTWC . The positions and intensities are best estimates of those quantities when the warning is issued. THESE ARE NOT BEST TRACKS - having not been reanalyzed in any systematic manner.

Ocean Heat Content & Forecast Track

Daily Oceanic Heat Content or Tropical Cyclone Heat Potential (TCHP) estimates were being provided by Gustavo Goni at the Physical Oceanography Division of the NOAA Atlantic Oceanographic and Meteorological Laboratory located in Miami, FL until July of 2008. Since that time the OHC has been provided by J. Cummings of the Naval Research Lab and is calculated from fields generated by the Naval Coupled Ocean Data Assimilation system (NCODA; Cummings 2005). The spatial grid spacing is 0.2 Latitude x 0.2 Longitude and the units of the estimates are given as kJ/cm^2. A detailed description of how the product is created, product archives and TCHP in other regions can be found at Gustavo's web discussing TCHP . A similar method is employed using the NCODA fields. Tropical cyclone forecasts, as described above, are plotted on values of ocean heat content for reference.

For tropical cyclones in favorable environmental conditions for intensification (i.e., vertical wind shear less than 15 kt, mid-level relative humidity >50 %, and warm SSTs [i.e., >28.5C])and with intensities less than 80kt, values of ocean heat content greater than 50 kJ/cm^2 have been shown to promote greater rates of intensity change.

4km Remapped Color Enhanced Infrared Imagery

Current imagery and loops of 4km remapped and color enhanced infrared (IR) imagery is displayed in an earth fixed coordinate system. IR imagery (~11 um) from five geostationary satellites are remapped to a common 4km resolution Mercator projection in an identical manner as the CIRA Tropical Cyclone Image Archive described in (Mueller et al. (2006) . These images are then centered and displayed using the nearest 5 degree latitude/longitude earth coordinate based on the most recent location and past 12-h movement. The images are also color enhanced with the coldest temperatures/highest clouds displayed as colored shades as shown in this color bar.

Geostationary imagery is available from GOES-East and Meteosat Second Generation (MSG; European Space Agency) in the North Atlantic, GOES-West and MTSAT (Japan) in the East Pacific, MTSAT in the West Pacific, and Meteosat-5 (European Space Agency) in the North Indian Ocean, and MSG, Meteosat-5, MTSAT, GOES-W in the Southern Hemisphere tropical cyclone basins.

AMSU Microwave 89GHz Imagery (4 km Mercator)

IR/WV/Microwave RGB (IR [R], WV [G], MI89 [B])

Passive Microwave Imagery (PMI) from low earth orbiting (LEO) satellites is routinely used in tropical cyclone analyses and forecast because several PMI channels can provide unique information about the location and organization of deep convection, liquid water, rainfall etc. that is often obscured by high clouds and cirrus in conventional Infrared (IR) and water vapor (WV) imagery. Since the late 1980’s PMI in the 85-91 GHz range has been used to determine the location and organization of deep convective elements, even through thick the thick cirrus often associated with developing TCs. IR and WV imagery, which are available from geostationary satellites, have also been routinely used to monitor the organization, location, and intensity of TCs and infer changes in the TCs near environment. In the operational setting these three types of satellite imagery are typically viewed and analyzed separately (i.e., individual PMI images, and loops of WV and IR imagery). To examine the utility of combining the information from these separate imagery products, we have developed a Red Green Blue (RGB) image product that combines IR and WV information from the global fleet of geostationary satellites with the 89-91 GHz channels from several LEO satellites that are available on the NESDIS operational servers. We have plans to display these RGB images on our local RAMMB TC-realtime web page and to potentially make these available to the NHC and Pacific proving ground activities.

1km Remapped Color Enhanced Infrared Imagery

Polar-orbiting satellites, because of their lower altitude orbits, can provide higher resolution imagery, but with limited temporal resolution. Infrared imagery from the NOAA operational satellites and from the NASA Terra and Aqua satellites are utilized in this product. To view imagery from several data sources imagery are remapped to a common Mercator projection with a 1km resolution. The enhancement is identical to that used for the geostationary IR imagery as shown above. Times and satellite are shown in the footer of each image.

1km Remapped Visible Imagery

Using the polar orbiting satellites described above, 1km Mercator remaps of visible imagery are created.

2km Natural Color Imagery

Natural Color imagery approximates the response of normal human vision, providing a depiction of the satellite-observed scene. When satellites have separate channels for red, green and blue portions of the spectrum natural color can be approximated using those channels as input. However, the green channel has few other practical uses other than for providing natural color capabilities and because of this reason is not one of the channels on the future GOES Advanced Baseline Imager. Fortunately, the green component of light can be approximated using near infrared channels and a training set of natural color scenes.

Here we show a comparison between natural color imagery made using an approximation to the green component and natural color created using the observed green component. NASA’s MODIS imagery is used to create these comparisons and the storm-relative tropical cyclone imagery shown here has been remapped to a Mercator projection with 2-km resolution. The purpose of doing so is to provide a visually intuitive depiction that is useful to experts and non-experts alike, improving the interpretation of various features such as vegetation, water bodies, clouds and snow, deserts, etc., based on usage of natural colors to highlight those features. This also shows the sort of natural color capabilities that will be available from the next generation GOES satellites.

Multi-Platform Tropical Cyclone Surface Wind Analysis

Currently, this product combines information from five data sources to create a mid-level (near 700 hPa) wind analysis using a variational approach described in Knaff and DeMaria (2006). The resulting mid-level winds are then adjusted to the surface applying a very simple single column approach. Over the ocean an adjustment factor is applied, which is a function of radius from the center ranging from 0.9 to 0.7, and the winds are turned 20 degrees toward low pressure. Over land, the oceanic winds are reduced by an additional 20% and turned an additional 20 degrees toward low pressure.

The five datasets currently used are the ASCAT scatterometer, which is adjusted upward to 700 hPa in the same manner as the surface winds are adjusted downward, feature track winds in the mid-levels from the operational satellite centers, 2-d flight-level winds estimated from infrared imagery (see Mueller et al 2006 ) and 2-d winds created from Advanced Microwave Sounding Unit (AMSU)- derived height fields and solving the non-linear balance equations as described in Bessho et al (2006). Past analyses also made use of the QuickSCAT scatterometer (i.e., prior to November 2009), but this satellite is no longer producing observations of surface vector winds.

Each of the input data are shown in subpanels following the analysis (i.e., storm-relative). Shown are AMSU winds, Cloud-drift/IR/WV winds, IR-proxy winds and Scatterometer winds; QuikSCAT, when available for past analyses (BLUE) and ASCAT (RED). All input data in these panels has been reduced to a 10-m land or oceanic exposure depending on the location (i.e., non-surface data has been reduced to a 10-m exposure).

How good are the wind estimates? Here is the verification based upon 2007 data . These statistics were based on 1) H*Wind data when available and 2) best track wind radii estimates from NHC. In interpreting the wind radii verification it is important to not that the zero wind radii are included in the verification, which both skews and inflates the MAE verification statistics. Note however detection is improved over climatology provided by Knaff et al. (2007).

Digital Dvorak Intensity Estimates

Using the infrared (IR) images collected as part of the CIRA tropical cyclone IR image archive, which are displayed in an earth relative format as a product on this web page. Center positions are extrapolated using the current position and the past 12-h mean motion vector. Tropical cyclone intensity estimates can be made using two temperatures derived from the IR imagery. The first is the warmest pixel in the eye, and second is the warmest pixel on the coldest circle between 24 and 111 km from the cyclone center. Using these values a Raw T-number can be created by using the locally developed Table That expands upon the table published in Dvorak (1984). Each T-number has an intensity, in terms of maximum 1-minute sustained winds, associated with it and can be converted to an intensity.

While Raw T-numbers give an estimate of how strong a given storm is, the quantity is noisy, and because it is an instantaneous measure does not properly account for the relatively slow decay process of tropical cyclone winds. To remove the noisy nature of the Raw T-numbers time averaging is employed to produce a 6-h running mean of the raw T-numbers. This 6-h running mean is considered the T-number associated with the current intensity if the 6-h running mean is not decreasing at more than 1.5 T-numbers per day. If the 6-h running mean is decreasing very rapidly, a maximum of 1.5 T-number per day decay rate is prescribed. This final value of the 6-h running mean with a decay rule applied is considered the current intensity number or CI. The CI, as with any T-number estimate, can be converted into a intensity. However, it is important to note that THIS TECHNIQUE IS ONLY VALID FOR STORMS OF HURRICANE INTENSITY (65 kt) OR GREATER.

The image shown on this web page shows the time series of warning intensity and the Digital Dvorak estimate of intensity at the top and the time series of raw T-number estimates, the 6-h running mean, and the CI at the bottom.

Dvorak, V., 1984: Tropical cyclone intensity analysis using satellite data.NOAA Technical Report NESDIS 11, 47 pp. [Available from NOAA/NESDIS, 5200 Auth Rd. Washington DC, 20233].

Advanced Microwave Sounding Unit (AMSU) - Based Intensity Estimates

The Advanced Microwave Sounding Unit or AMSU, which is an instrument on the NOAA operational polar-orbiting satellites, has the capability to make temperature soundings. Using a combination of AMSU-based soundings, the hydrostatic relationship, and statistics, a tropical cyclone intensity estimate can be made. The methodology used here is discussed in Demuth et al (2004) and updated in Demuth et al. (2006). Estimates are created by the National Centers for Environmental Prediction and the estimates as well as other products are available for the last two days at NCEP Central Operations. While overall statistics are comparable with the Dvorak technique, this method is most useful and accurate for tropical cyclones with intensities less than ~90 kt. Shown in this product are time series of the operational warning intensities versus the AMSU-based intensity estimates.

AMSU-Based Azimuthal Mean Radial/Height Cross Sections

Using the AMSU-derived azimuthally averaged temperature and height files radial/height cross sections of temperature and tangential wind are created (see Demuth et al (2004) ). The tangential wind field is derived using the 2-d gradient wind equations. Note that the resolution horizontal of the AMSU instrument results in a smooth temperature field and an unrealistically low tangential wind speeds. These images are useful in determining the thermal structure of the tropical cyclone.

Storm Relative 16km Microwave-Based Total Precipitable Water Imagery

The relative lack of environmental moisture around a tropical cyclone can adversely affect the deep convection and negatively impact the storm and result in weakening. Luckily there is several low earth orbiting satellites that provide estimates of the amount of water vapor in the atmospheric column, commonly referred to a total precipitable water (TPW). TPW estimates from a single satellite platform, however, often suffer from inadequate temporal coverage and poor refresh rates. To partially rectify this issue, the information from three Advanced Microwave Sounding Units (AMSU) on NOAA satellites and five Special Sensor Microwave Imagers (SSMI) on DOD satellites are combined via a blending algorithm described in Kidder and Jones (2007). Such a product has a refresh rate of approximately 6 hours and a spatial resolution of approximately 16km. This product shows the TPW around the tropical cyclone and to further enhance its utility the images are centered on the current storm location and when looped show TPW features moving to and from the storm center.

Storm Relative 16km Geostationary Water Vapor Imagery

To compliment the 16km storm relative TPW product listed above, water vapor imagery, with a spectral weight near 6.7 um is displayed with the same resolution, projection, and storm relative geometry. Water Vapor imagery is helpful in determining the location of deep convection, indicated by the coldest pixels, relative upper-level moisture content in areas devoid of deep convection, and upper-level atmospheric motions via animation of these images. The imagery can be used to infer favorable and unfavorable regions of environmental forcing (e.g., areas of increased vertical wind shear or atmospheric subsidence).

Storm Relative 1km Geostationary Visible Imagery

The current suite of geostationary satellites provides visible imagery during daylight hours at higher resolution than many of the infrared channels. Such imagery is useful, especially when animated, for position estimation and monitoring the degree of convective organization. The native visible imagery has been remapped to a one-km Mercator projection and the digital data has been stretched over its full range - allowing a more esthetically pleasing appearance. The center location is based on the last operational position estimate and the previous 12-hr motion.

Multi platform Tropical Cyclone Kinetic Energy and Intensity

From the Multi platform satellite wind analysis discussed above a flight level (~ 700 hPa) Kinetic Energy is calculated within 200km of the cyclone center. The calculated KE is then categorized (0-5) so that their probability distribution is identical to the Saffir- Simpson Hurricane Intensity Scale (0-5). The KE is then plotted versus the maximum surface wind from these same wind analysis and provided every six hours. Tropical cyclones tend to grow as they weaken, but this is not always the case and large storms typically have larger values of KE and thus are more destructive when they affect land. This product allows the real-time monitoring of the potential destructive potential of a given storm and allows inter comparison with past events either produced on this web page or from actual flight level wind data. The methods for calculating and categorizing the KE as well as analyses of several past events are described in Maclay et al. (2008).

2km Storm Relative IR Imagery with BD Enhancement Curve

The same infrared imagery shown in the earth relative framework is displayed in a storm relative framework, with a 2km resolution and enhanced with the "BD Curve" which is useful for directly inferring intensity via the Dvorak Enhanced IR (EIR) technique. Scaling is provided by two lightly hatched circles around the center. The two circles have radii of 1 and 2 degrees latitude, respectively.

Multi platform Tropical Cyclone MSLP and Maximum Winds

Minimum Sea Level Pressure is calculated directly from the azimuthally averaged gradient level tangential winds produced by the multi platform tropical cyclone wind analysis. The circular domain for the numerical integration has a 600km radius. The pressure deficit resulting from the integration is then added to an environmental pressure. The environmental pressure (Penv) is interpolated from NCEP analyses in a circle 600 km from the cyclone center. The maximum surface winds produced by the analysis are also shown.

AMSU Area-Averaged Wind Shears and Layer Means

These products use the balanced 3-D wind field derived from the AMSU temperature retrievals to estimate the area averaged vertical wind shear and mass weighted deep-layer mean wind in two layers (200 to 850hPa and 500 to 850Hpa). For these calculations the area averaging is calculated in the area contained within 0 to 600km from the center of the cyclone. These are displayed for each AMSU retrieval time available. These may be useful for detecting rapid changes in the synoptic wind field. The reliability of the vertical wind shear estimates is documented in Zehr et al. (2008).

IR-based TC size

Tropical cyclone size, the radius of where the TC wind field is indistinguishable from the background flow in a climatological environment, is empirically estimated from IR imagery and storm latitude. Principle components of the storm centered, azimuthally averaged IR brightness temperatures and the sine of the latitude have been regressed on the azimuthal mean tangential winds around TCs at 500k radius (V500) using a 1995-2011 Atlantic and East Pacific data set. Using the same dataset the climatological TC size (as defined above),radial decay of tangential winds beyond 500 km radius and V500 has also been estimated. Combining the V500 estimate along with the climatological TC information allows us to estimate TC size. This TC size metric is reported in units of degrees latitude. More information on how to calculate this metric can be found in Knaff et al. (2013), which is being reviewed for publication in the Journal of Climate.

Time Series of the Simplified Holland B parameter calculated from the TC Vitals

The simplified Holland B parameter [SHB, Knaff et al. (2010)] is a powerful TC structure diagnostic that is easily calculated from routinely available data. The SHB is related to the shape of the tangential wind profile beyond the radius of maximum wind (RMW), and is insensitive to variations of radius maximum winds. Large values of SHB (order 2.25) imply compact tangential wind profiles while, small values (<1.0) are related to broad tangential wind profiles. SHB also increase with both the intensity and radial extent of the wind field. It is noteworthy that TCs that are weak have a generally large range of SHB, between 0.5 and 2.25, while very intense TCs have SHB values in a narrow range between 1.75 and 2.3. More details of the sensitivity of SHB to TC structure are provided in Knaff et al. (2010). Here we have calculated SHB from the initial tropical cyclone conditions provided by NHC and JTWC (sometimes referred to as TC vitals or the TC bogus) as a function of time, indicated by the red line. The time series provides information on the structural evolution of the TC. The empirically derived lower and upper bounds of the SHB as a function of intensity are also provided by the thin black lines in the figure.

Day/Night Visible Imagery VIIRS

This product displays storm relative imagery from Joint Polar Satellite System (JPSS) spacecraft, the Suomi NPP (National Polar-orbiting Partnership), launched on October 28, 2011. Polar-orbiting satellites, because of their lower altitude orbits, can provide higher resolution imagery, but with limited temporal resolution. Imagery from Visible Infrared Imaging Radiometer Suite (VIIRS) is used for this product. VIIRS data are collected for each SNPP pass over tropical cyclone center. This product creates a loop combining two band from VIIRS. For the day-time images it uses the high resolution visible band (I01, 375 m resolution at nadir). For the night image the unique VIIRS Day Night Band (DNB) is used (742 m resolution across the swath). Both images are remapped to Mercator projection at their native resolution, and 6 by 6 degrees latitude/longitude box is displayed around the storm center interpolated from latest available ATCF data. Additional information about VIIRS is available at http://rammb.cira.colostate.edu/projects/npp/.

Enhanced Infrared (IR) VIIRS

This product displays storm relative imagery from Joint Polar Satellite System (JPSS) spacecraft, the Suomi NPP (National Polar-orbiting Partnership), launched on October 28, 2011. Polar-orbiting satellites, because of their lower altitude orbits, can provide higher resolution imagery, but with limited temporal resolution. Imagery from Visible Infrared Imaging Radiometer Suite (VIIRS) is used for this product. VIIRS data are collected for each SNPP pass over tropical cyclone center. The image from M15 longwave IR band is remapped to Mercator projection at it's native 750 m resolution, and 6 by 6 degrees latitude/longitude box is displayed around the storm center interpolated from latest available ATCF data. The image is color enhanced to emphasize the coldest temperature/highest clouds. Additional information about VIIRS is available at http://rammb.cira.colostate.edu/projects/npp/.