A Reanalysis of the 1916, 1918, 1927, 1928, and 1935 Tropical Cyclones of the North Atlantic Basin

1. A Reanalysis of the 1916, 1918, 1927, 1928, and 1935 Tropical Cyclones of the North Atlantic Basin A Master’s Defense By David A. Glenn May 12th 2005

2. Introduction • Thesis Objectives • What is a tropical cyclone or hurricane? • What is the hurricane database (HURDAT), how is it used, and why does it need revision? • Data used in the reanalysis • Methods for determining track and intensity • Changes for 1916, 1918, 1927, 1928, and 1935 • Results of the reanalysis • Results of the Accumulated Cyclone Energy (ACE) index

3. Objectives • The purpose of this project is to reanalyze HURDAT for the years of 1916, 1918, 1927, 1928, and 1935. This involves revising the original HURDAT record by changing the track and intensity of tropical cyclones in the original hurricane database. II. The second objective is to assess the effects of revising HURDAT on the accumulated cyclone energy (ACE) index. The computed ACE index values indicate the amount of tropical activity; therefore, if major alterations are suggested for HURDAT then the changes will be apparent in the ACE index computations.

4. The Hurricane • A hurricane is defined as a warm core non-frontal synoptic-scale cyclone possessing winds greater than 64 knots. • Low-level closed circulation about a well defined center. • Maintained through latent heat of evaporation of warm ocean water. Source: NOAA COMET

5. Saffir-Simpson Scale

6. HURDAT • The National Hurricane Center houses the North Atlantic Basin’s HURricane DATabase (HURDAT) • Track and intensity estimates provided every 6 hours • Originally designed for statistical tropical cyclone guidance for the Apollo Space program (1960). • Free online at: www.nhc.noaa.gov/pastall.shtml

7. HURDAT Uses: - Aid in forecast development and verification. - Climate trend assessment – long term trends, seasonal forecasts, etc. - Building code standards and insurance rates for coastal communities - Risk assessment for emergency managers (recurrence intervals) HURDAT was not originally designed for all of these uses…

8. Why Revise HURDAT? • Why revise? - HURDAT contains many systematic and random errors (Neumann 1994) - Limitations in the original hurricane database Once daily estimates before 1930. - Advances in the understanding of hurricanes and analysis techniques - Lack of exact hurricane landfall parameters (i.e. location, time, intensity, central pressure, storm surge, and radius of maximum winds)

9. Beaufort Scale Source: Fitzpatrick, 1999

10. Random Error • Original classification errors - 28320 10/30/1935 M=10 6 SNBR= 624 NOT NAMED XING=1 SSS=2 L 28325 10/30* 0 0 0 0*326 609 35 0*328 618 35 0*330 628 40 0* 28330 10/31*331 637 40 0*333 645 45 0*334 653 50 0*335 666 55 0* 28335 11/01*337 681 60 0*337 697 60 0*336 712 65 0*335 726 70 0* 28340 11/02*332 738 70 0*328 750 70 980*322 757 70 0*316 759 70 0* 28345 11/03*309 760 70 0*302 760 70 0*295 761 70 0*286 764 65 0* 28350 11/04*277 771 65 0*270 779 65 0*265 787 65 0*258 803 65 973* 28355 11/05*253 811 65 0*249 825 65 0*249 835 65 0*251 843 65 0* 28360 11/06*252 850 60 0*255 857 60 0*260 863 55 0*264 867 50 0* 28365 11/07*268 870 45 0*275 871 40 0*280 869 35 0*281 858 30 0* 28370 11/08*278 847 25 0*277 842 20 0*276 837 15 0*275 834 15 0* 28375 HRCFL2 This is an example of a random error that is easily corrected through the reanalysis process. Category 2 = 83-95 kt.

11. Errors in HURDAT

12. Anemometer Bias Prior to the 1920’s, Robinson 4-cup anemometers were used that generally overestimated winds speeds greater than 30 knots (Fergusson and Covert, 1924). For example, a minimal hurricane force wind of 64 kt actually reduces to 50 kt after bias correction. Most anemometers were compromised or destroyed before sampling the highest winds.

13. Original HURDAT Limitations • From the period 1886 to 1930, the original HURDAT was created from a once daily 12 GMT track and intensity estimate (Jarvinen et al, 1984). The 00, 06, and 18 GMT track and intensity estimates were interpolated from two days 12 GMT estimates. • Problematic for storms undergoing rapid intensification or rapid decay.

14. ACE Index • Accumulated Cyclone Energy (ACE) index is a tool used to quantify the amount of tropical activity. • Uses wind velocities in HURDAT: Σ [(55 kt)2 + (60 kt)2 + (65 kt)2 + (75 kt)2] = 16475 kt2. • The ACE index is considered a physically and statistically reasonable measure of the overall tropical activity for a given hurricane season (Bell et al, 2000).

15. Reanalysis Steps 1.) Gather all available raw data into a single database 2.) Determine track 3.) Determine intensity 4.) Document revisions (metadata file) Each day of each storm is reanalyzed. The process is usually fairly tedious and takes 2-3 hours to discuss the changes for a single storm.

16. Data Sources • Comprehensive Ocean-Atmosphere DataSet (COADS) – (Woodruff et al, 1987) • Monthly Weather Review (MWR) – American Meteorological Society • Original Monthly Records (OMR) – Station Data from U.S. Weather Bureau or partner observation stations • Historical Weather Maps (HWM) – Created by the U.S. Navy and U.S. Weather Bureau • National Climate Data Center – individual ship and station observations • Historical hurricane reports – Barnes (1998a,b), Connor (1956), Dunn and Miller (1960), Ho (1989), Ho et al (1987), Ludlum (1963), Perez (2000), Tannehill (1938), Tucker (1982)

17. COADS Source: Woodruff et al, 1987

18. MWR

19. MWR

20. MWR

21. OMR

22. HWM The example to the right is an annotated Historical Weather Map. Some raw data are gathered from the HWM but it is mainly used as the synoptic background for plotting all raw data from the sources of COADS, MWR, OMR, and other historical reports. Observations are plotted for the time interval 10-14Z to maximize data near the synoptic time.

23. Data Aggregation and Conversion Wind units are converted to knots and barometric pressures are converted to millibars to be consistent with current analyses.

24. Track Determination The process for defining the center of a tropical cyclone from observed winds. Two ship observations (indicated by the red wind barbs) roughly indicate the tropical cyclone center (where the two black lines cross) assuming cyclonic flow with a 20o inflow angle (Landsea et al, 2004).

25. Time-Series Low-Pressures Time-series low-pressures maps are useful for landfalling tropical cyclones. The central path follows the lowest pressures.

26. Intensity Determination • It is important to locate the nearest lowest barometric pressure or observed wind speed (to the perceived center). When the analyst does not have observed wind speed, atmospheric pressure measurements (central or peripheral) can be used to provide estimates of the maximum sustained wind speeds in a tropical cyclone. • Pressure-wind relationship • Radius of maximum winds (RMW) • Inland Wind Decay Model • Collaborating pressures

27. Atlantic Pressure-Wind Relationship GMEX Wind (kt)=10.627*(1013-Po)0.5640 Sample size =664; r=0.991 < 25°N Wind (kt)=12.016*(1013-Po)0.5337 Sample size =1033; r=0.994 25-35°N Wind (kt)=14.172*(1013-Po)0.4778 Sample size =922; r=0.996 35-45°N Wind (kt)=16.086*(1013-Po)0.4333 Sample size =492; r=0.974 Kraft Wind (kt)=14.000*(1013-Po)0.5000 Sample size =13

28. RWM • Vickery et al. (2001) derived an equation for the radius of maximum winds (RMW) of north Atlantic tropical cyclones expressed in terms of central pressure (Po), environmental pressure (Pn), and latitude (L): ln(RMW) = 2.363 – 0.00005086*( Po - Pn)2 + 0.0394899*(L) • RWM of 25 to 50 percent less than climatology had an adjustment of five knots while systems that had extremely smaller RMW (greater than 50 percent) were adjusted by 10 knots (Landsea et al, 2004).

29. Kaplan and DeMaria (1995): Inland Wind Decay Model • The Inland Wind Decay Model was used to determine the best track after landfalling tropical cyclones. • Only used in the absence of observed winds. • Designed for landfalling tropical cyclones over the southeastern U.S. where nearly all the regions within 150 nmi of the coast have elevations less than 650 ft. • Not applicable for higher terrains such as Cuba, Hispaniola, and Mexico.

30. Original 1916 HURDAT

32. 1916 Revisions

33. 1916 Revisions cont.

36. 1918 Revisions

39. 1927 Revisions

42. 1928 Revisions

45. 1935 Revisions

46. Metadata It is estimated that the storm became a hurricane on September 1st around 12 UTC just south of Andros Island in the Bahamas. Over the next 24 hours the system nearly doubled in intensity from 65 kt to 120 kt on the 2nd. A central pressure of 924 mb at 21 UTC of the 2nd implies winds of 132 kt from the southern pressure-wind relationship. 140 kt is chosen for 18 UTC HURDAT as later evidence suggests a smaller than usual radius of maximum winds (RMW) for this system. Available observations estimate landfall to have occurred near 02 UTC on the 3rd at Craig Key. Intensity at landfall has been estimated from pressure observations at Craig Key [892 mb] indicating 155 kt winds from the southern pressure-wind relationship or 140 kt from the subtropical pressure-wind relationship. An average of these two pressure-wind relationships (since the system was near the border of the two) suggests winds of around 148 kt. Regarding the probable RMW at landfall in the Keys, "it is estimated that the calm center was perhaps 8 miles in diameter" (MWR). Available observations suggests the RWM to be 6 nmi (Ho et al). RMW were also noted as 6 nmi from Schwerdt et al. 6 nmi RMW is smaller than what might be expected from climatology of this central pressure and landfall latitude (9-10nmi - Vickery et al). Thus this tiny RMW suggests a significant boost from the standard pressure wind relationship and 150 kt is chosen for 00 UTC in HURDAT. Peak observations of lowest pressure (and implied highest winds) were observed at 02 UTC and therefore an addition to the normal HURDAT 6 hour time interval is suggested such as in the case with Hurricane Andrew (1992). 160 kt is chosen for 02 UTC in HURDAT. This maintains the hurricanes intensity as Category 5 but increases its previous peak intensity from 140 kt to 160 kt. After passing the Keys, the hurricane moved toward the northwest and eventually north on the 4thbefore making its second landfall in northwest Florida. An observed peripheral pressure of 941 mb early on the 4th suggests at least 119 kt winds from the Gulf of Mexico pressure-wind relationship. 125 kt is chosen for HURDAT at 00 UTC. Metadata can take several hours per storm and is the bulk of the work for this thesis.

47. Reanalysis Results Synopsis In general, track estimates during the 1910’s, 1920’s, and 1930’s needed minor revisions. Intensity estimates for the period saw the greatest change with the single largest change of 30 knots occurring in 1916 and 1927. The addition of four tropical storms to the original HURDAT record was offset by the deletion of three tropical storms, increasing the total number of storms for the period to 41. Only one storm had no revisions in intensity from the original HURDAT. No major changes were found for systems that made landfall in the United States. A new database for tropical cyclones that affected the United States was also completed allowing future HURDAT users to obtain more information about such tropical cyclones.

48. Tropical Cyclone Activity • Klotzbach and Gray (2004) - ‘normal’ 9.6 named systems, 5.9 hurricanes (2.3 major hurricanes) • Bell et al. (2000) - ACE Index 6.5 to 10*105 kt2 - Based on climatology from 1950-2000

49. ACE

50. Discussion • Mexico data needs to be utilized. • This process can be repeated if newly discovered data becomes available. • The project can also be utilized in other basins (e.g. West Pacific Ocean) • This research will be evaluated by the Best Track Change Committee for final acceptance of revisions to HURDAT.