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Best Track Re-Analysis Activities at the National Hurricane Center

NATIONAL CENTERS FOR ENVIRONMENTAL PREDICTION. Best Track Re-Analysis Activities at the National Hurricane Center. JACK BEVEN. NATIONAL HURRICANE CENTER. WHERE AMERICA’S CLIMATE AND WEATHER SERVICES BEGIN. Outline. Overview of re-analysis activities

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Best Track Re-Analysis Activities at the National Hurricane Center

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  1. NATIONAL CENTERS FOR ENVIRONMENTAL PREDICTION Best Track Re-Analysis Activities at the National Hurricane Center JACK BEVEN NATIONAL HURRICANE CENTER WHERE AMERICA’S CLIMATE AND WEATHER SERVICES BEGIN

  2. Outline • Overview of re-analysis activities • Recent work in the early-recon period in the Atlantic • The test bed Eastern Pacific re-analysis

  3. Re-analysis overview • Chris Landsea’s Atlantic re-analysis project has ‘completed’ the 1851-1930 period. • The 1931-1953 period has been partly examined. • While great progress has been made, the project has moved slower than originally planned. The progress is expected to slow further as the project reaches periods with more data. • No period has been truly ‘completed’. New data and new potential storms are still being found for the 1851-1930 period.

  4. Some re-analysis issues • Many data gaps for older systems could potentially be filled. The search for old data/anecdotal accounts is not complete, especially in the Caribbean countries and Central America. This requires people willing to perform data mining in libraries and archives. • Changes in and problems with instrumentation must be watched for and documented. For example, pre-1928 four-cup anemometers in the United States had a high speed bias in hurricane-force winds. • Re-analysis of the aircraft reconnaissance period will deal with changes in flight procedures, instrumentation, and data interpretation. Standards for this need to be worked out. • Standards also need to be set on how satellite data (e. g. Dvorak estimates) should be used. For example, how many Dvorak analyses per best track time is optimum?

  5. The NHC Best Track Change Committee • Excerpt from the committee charter: “The final “best-tracks” are prepared by the National Hurricane Center (NHC) hurricane specialists at the conclusion of every Atlantic and eastern north Pacific tropical cyclone. These tracks represent the best estimate of tropical cyclone position, intensity and status every six hours during its life cycle. They are based on a comprehensive analysis of all available observational data. Once completed, these tracks are added to the historical tropical cyclone database for each basin. These files (1851 to the present for the Atlantic, 1949 to the present for the eastern north Pacific) are used at NHC for verification of forecasts and other internal applications. They are also used extensively by the research, academic and insurance communities, as well as the media and the public. The best-track files are not static, but rather represent the best current estimates for tropical cyclone track and intensity, given the observations and science available at the time. Newly acquired observations, re-interpretation, or re-analysis may indicate changes to these tracks. Such changes must be dealt with in an organized and well-documented manner.”

  6. The NHC Best Track Change Committee • The committee is the ‘keeper’ of the Atlantic and Eastern North Pacific best track records. It is the committee‘s job to analytically examine all proposed changes to the records and decide whether they should be incorporated or rejected. This includes modifications to existing storms, addition of new storms, and deletion of existing storms that may not have actually met tropical storm/ hurricane criteria.

  7. Reanalysis Steps • Obtain all raw data (and center fixes) into a single database. • Plot all surface obs onto synoptic maps at least once daily. • Choose track/intensity from synoptic maps and center fixes. • Explain track and intensity determinations in a metadata file, highlighting reasons for large changes to track and intensity • Look for “missing storms” and follow similar procedure • When complete, the following files should be stored in the folder for that storm (or year): • A spreadsheet - database containing all raw obs • A metadata file (described above) and your 6-hourly best track data • All synoptic maps utilized • All info from all sources/references utilized

  8. Rules for Determining Intensity • If you have a central pressure, use p-w relationship • If you know RMW, Penv, size, and/or speed of the cyclone, add or subtract 5 or 10 kt to the p-w relationship as appropriate • In the absence of a central pressure, assign a wind speed 5 kt higher than the highest wind ob available • If you have a peripheral pressure ob, you at least know a lower bound for the intensity from p-w relationship • Continuity if lack of data (to a point). But no changes to HURDAT if no data, because interpolating through data gaps is problematic.

  9. Reanalyzing Intensity: 1953 Hurricane Carol Portion of Original HURDAT track for Hurricane Carol (1953). Carol Key observations: • 9/1 18Z: Ship 60-65 kt NE (x nmi) from center. • Should choose at least 65-70 kt. • Chose 90 kt (55 kt) at 18Z based on 944 mb 18 hours later. • 9/2 13Z: AC – 944 mb central pressure = 119 kt. • Chose 120 kt (75 kt) at 12Z. • 9/3 18Z: AC – 929 mb central pressure = 133 kt. • Chose 140 kt (130 kt) at 18Z due to tiny RMW (3 nmi) **(eye diameter)** and fast forward speed (16 kt). Pressure-wind relationships used are southern-intensifying subset of Brown et al. Red numbers are the intensities listed in the original HURDAT

  10. Chose Intensity: New Storm with no AC New to HURDAT: Oct 12, 12Z map 31895 10/11/1944 M= 7 12 SNBR= 707 NOT NAMED XING=0 31896 10/11*355 400 35 0*355 400 35 0*355 400 40 0*355 400 45 0* 31897 10/12*356 400 50 0*357 400 60 0*360 400 70 0*366 400 70 0* 31898 10/13*375 399 70 0*383 395 60 0*390 385 50 0*397 365 50 0* Key observations: Determine intensity at 10/12 12Z: -Highest wind: 70 kt at 14Z -Lowest p: 996 mb at 11Z cp <996 mb -> wind>53 kt -Would choose 75 kt if adhere to methodology of choosing 5 kt above highest observed wind Chosen 70 kt (subject to revision) b/c lowest p was 996 mb with dense data. (65 & 70 kt ship far from center)

  11. Track analysis with recon fixes All center fixes compiled Fixes plotted and interpolated to 6-hourly positions Ship and station data plotted against aircraft data Final revised positions are a subjective consensus of all data When lack of data, significant changes are not implemented 78W 76W 74W 1953 Barbara 34N 32N 30N 1948 Storm #3 Radar fix Penetration fix

  12. Early Aircraft Recon Data • Position: Center fixes and navigation accurate to within 30 nmi on average • Surface wind speeds (estimated visually) and flight-level wind speed measurements were both highly inaccurate and displayed a high bias • Aircraft central pressures (when available) are used to determine intensity via the Brown et al. (2006) pressure-wind relationships • Major hurricanes were rarely penetrated in 1944-53 – central pressures below 950 mb were extremely rare

  13. Aircraft data can cause problems! Post flight summary 9/2/1952 Storm Baker: “Entered eye…min pressure 993 mb…max wind encountered 130 kt”

  14. Eastern Pacific Re-analysis Motivation • There are known problems with the eastern Pacific HURDAT. • Severe discontinuities in the data (around the late 1960’s and around the time NHC assumed responsibility in 1988) • Need to ensure a consistent application of analysis across the data set. • We want to get it right! It’s our job to do so as caretakers of HURDAT. • Utilized heavily in climate studies

  15. Scope and Data of the EPAC Re-analysis • Re-analysis generally covers the pre-1988 period (before NHC assumed operational responsibilities for the basin) • Primary data sources include NOAA CLASS satellite imagery, ICOADS, and Mexican surface observations (in NCDC’s EDADS data base) • NAVY “best tracking” discovered and will be utilized • Tracks in the 1950’s and 1960’s are too smoothed • Boxes in NCDC basement contain archived data useful for the re-analysis • Data have not been organized nor digitized • Thorough review of the literature (e.g., Monthly Weather Review, Mariners Weather Log) and Historical Weather Maps to discover any missing systems • Searching Mexican periodicals for evidence of missing Mexican landfalls or data regarding known landfalls

  16. Issue - Oversimplification of Tracks? #1 #2 #1 #2

  17. An Early Look at Potential HURDAT Errors HURDAT Position Socorro Is.. T4.5/5.5 in “re-analysis”. HURDAT: 115 kt Position in HURDAT 0.5° to the east Genesis at this time? Dreaded Pinhole Eye. HURDAT: 65 kt

  18. Hurricane Max, 1987 Current HURDAT 08/2345 0.2 1.0 D 1.0 1.0 1.0 1.0 1.5 D 1.0 2.0 1.5 1.5 09/0545 0.3 Missed RI and subsequent arrested development 25 2.5 D+ 1.5 2.0 2.0 2.0 09/1145 0.5 30 09/1745 0.45 2.5 D+ 1.5 2.5 2.0 2.0 35 D+ 2.5 2.5 2.5 2.5 09/2245 0.4 2.5 45 D+ 2.5 3.5 3.0 3.0 3.0 0.65 10/0545 45 D 3.0 3.5 3.0 3.0 3.0 0.7 10/1145 50 0.7 D 3.0 3.0 3.0 3.0 3.0 10/1645 60 D 3.5 4.0 3.5 3.5 0.5+ 10/2345 3.0 3.5 >1.5 65 3.0 0.6 0.5+ 3.5 D 4.0 3.5 3.5 3.5 11/0545 70 LG 4.5+ 0.0 4.5+ D+ 4.5 6.0 4.5 4.5 11/1145 80 D+4.5 5.0 5.0 5.0 5.5 -0.5 B 11/1745 5.0 5.0 90 0.5 D+5.0 6.0 6.0 6.0 B 5.5 6.0 6.0 11/2345 100 5.0 5.0 D+6.0 5.5 5.5 6.0 -0.5 12/0545 B 5.5 105 5.0 5.0 D- 5.0 5.0 5.0 6.0 -0.5 5.5 B 12/1145 115 0.5 6.0 6.0 5.5 B D- 5.5 6.0 6.0 6.0 12/1745 125 B S 6.0 6.0 6.5 6.5 5.5 1.0 6.5 6.5 12/2345 135 13/0545 6.0 1.0 W 7.0 7.0 D7.0 - 7.0 7.0 135 LG 5.0 1.0 D7.0 - 6.0 7.0 6.0 6.0 13/1145 135 W+ 4.5 5.0 5.5 6.5 4.5 0.0 MG 4.5 4.5 13/1745 Vis CDO = 5.5 135 W 5.5 5.0 5.5 6.5 LG 5.0 0.5 5.5 5.5 13/2345 115 4.5 4.5 W+ 5.5 5.0 4.5 5.5 14/0545 DG 4.5 0.0 105 DG W+ 5.5 4.0 4.5 5.5 14/1145 4.0 4.0 Missed Rapid Weakening 100 W+ 5.0 4.0 4.0 4.5 4.0 4.0 14/1745 MG 90 4.0 4.0 W+ 5.0 4.0- 4.0 4.5 MG 14/2345

  19. Hurricane Max, 1987 90 MISSING 14/2345 75 15/0545 0.5 2.5 W+ 4.0 3.0 3.0 4.0 65 2.5 <3/4 15/1145 W+ 4.0 2.5 2.5 3.5 45 15/1745 0 W+ 3.0 0.0 2.0 3.0 35 15/2345 0 W+ 3.0 0.0 1.5 2.5 30 TWTC 16/0545 25 16/1145 TWTC

  20. Available Satellite Imagery and Issues • NOAA CLASS data: McIdas AREA files are 8-bit, half hourly, and has a “4 km” resolution • Calibration issues: N-AWIPS can only display 7-bit data and thus only half of the 256 possible colors • Other software may display more but smoothing algorithms overly refine data • Resolution: some of the imagery is of uneven resolution (e.g., 8km in latitude but 4 km in longitude) • All imagery remapped to 4 km • Missing or no data: occasional gaps, some of poor quality; imagery becomes less frequently available earlier • 1977 has no digitized imagery • Other issues? TBD • Polar Orbiter data to be used to supplement imagery or fill in gaps

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