Ryan N. Maue's Seasonal Tropical Cyclone Activity Update
Houston Chronicle Article on Tropical Storms and Global Warming -- Link
North Atlantic Hurricane Season slowest since 1997 -- Figure
Global and Northern Hemisphere Tropical Cyclone Activity remains near 30-year historical lows
-- three years in a row now of considerably below-average activity globally. -- Figure
Consequence of the transition from La Nina to El Nino during the past year
The best of 2009: Hurricane Bill, Hurricane Fred, Hurricane Rick, Super Typhoon Melor, Typhoon Parma
Oct 29: The North Atlantic hurricane season has not produced a storm in over 3-weeks and, if no more develop, the season overall would rank as the slowest since the El Nino year of 1997. Hurricanes Bill and Fred accounted for over 82% of the Accumulated Cyclone Energy [ACE**] -- a metric that combines intensity, duration, and frequency of hurricanes and tropical storms during a year. The remaining storms were weak, rather short-lived and unremarkable. Indeed, the Accumulated Cyclone Energy [ACE] of 44 ranks among the slowest during the past half-century. Elsewhere, the Northern Hemisphere and Global ACE when calculated either with 12- or 24-month running sums, remains just above historical 30-year lows. Indeed, the global ACE sunk to record low levels during the early summer prior to the typhoon activity in the Western Pacific and the hurricane activity in the Eastern Pacific. While it may seem like the world has experienced considerable tropical cyclone activity lately, 2009 as a whole is still well behind normal or climatology. The previous Southern Hemisphere cyclone season including the Southern Indian and Pacific Oceans along with the Australian region produced historically low levels of ACE (from Oct 2008 - Apr 2009). So a global sum during the past 12 or 24 months will simply show the depressed tropical cyclone activity experienced.
This is a natural consequence of the rather unusual flip from strong La Nina to El Nino conditions during the past calendar year, which did not happen at all during the period of 1976-2006 as indicated by the MEI-ENSO INDEX (LINK). It is expected by NOAA and others that the current-El Nino is locked in for the rest of winter 2009-2010 and may indeed strengthen. This would suggest enhanced typhoon activity in the Western Pacific throughout the rest of the fall and winter which will necessarily increase the NH ACE. The Southern Hemisphere TC season may begin at any time now, but most activity is experienced between January and March.
**Note: The Accumulated Cyclone Energy metric combines frequency, duration, and the intensity of tropical cyclones into one value that can be calculated from historical storm records as well as current operational center (i.e. NHC) advisories. The ACE is simply the wind speed squared (times 10^4 kts^2) for each 6-hour storm location and intensity estimate -- added up for an entire season or whatever period you wish to define. CLIMO based upon 1979-2008 climatology.
Important Links
Great Depression ! Global tropical cyclone energy remains near 30-year lows !
Figure: 12-month running sums of Accumulated Cyclone Energy for the entire globe during the past 31-years -- 1979 to October 29, 2009 (current). Average is 769.With the Northern Hemisphere Tropical Cyclone (TC) seasons winding down in the Eastern Pacific and North Atlantic, it is as good as time as any to take account of what the Earth has offered during the past 12-months in terms of TC Accumulated Cyclone Energy (ACE). Since the last Southern Hemsiphere season was quite uneventful with well-below normal ACE, and the continued Northern Hemisphere inactivity, the sum of the two = global ACE reached record low values in the early summer of 2009 and has slightly recovered only just recently.
The Raw Data -- Accumulated Cyclone Energy (ACE) valid November 11, 2009 00Z
The current ACE represents the tropical cyclone activity from January 1, 2009 until the date indicated. This is readily compared to the YEARLY value which is the previous 30-year average from Jan 1 - Dec 31 or the calendar year. The values through October 31 and November 30 represent the previous 30-year average as well with the average October ACE indicated in the last cell. There is considerable year-to-year variability across the basins, of which understanding motivates the updating and maintainance of this site.
| BASIN | 2009 CURRENT | 30-YR AVG ALL YEAR |
30-YR AVG THRU NOV 30 |
30-YR AVG NOVEMBER |
| N Hemisphere | 412.765 | 563 | 543 | 50 |
| N Atlantic | 51.985 | 106 | 105 | 6 |
| W Pacific | 228.045 | 309 | 292 | 38 |
| E Pacific + CPAC | 127.25 | 132 | 132 | 2 |
| N Indian | 5.485 | 17 | 15 | 5 |
| S Hemisphere | 107 | ~210 | -- | -- |
Comparisons through October 29
FIGURE: What is the current state of tropical cyclone activity compared to the same date during
the past 30-years? The bar-chart shows the calendar-year-to-date Northern Hemisphere ACE experienced from January 1 - October 29 during
the past three decades. The 2009 value is 397 and is clearly among the less-active years. Since the North Western Pacific accounts
for 51% of the Northern Hemisphere total on average, it is well-correlated with the NH total since 1979 (r=0.81). However, the
North Atlantic ACE since 1979 is not well-correlated with the NH total (r=0.24).
The following comparison table
highlights the GLOBAL,
SOUTHERN HEMISPHERE, and NORTHERN
HEMISPHERE totals for the previous 12 and 24-months, respectively.
| BASIN | CURRENT 12 [24] MONTH TOTAL | 30-YR AVG 12 [24] MONTH TOTAL |
| NORTHERN HEMISPHERE | 422 [882] | 563 [1126] |
| SOUTHERN HEMISPHERE | 103 [296] | 206 [412] |
| GLOBAL TOTAL | 525 [1178] | 769 [1538] |
Current Global Tropical Cyclone News & Updates
October 29: With October over in 3-days, here is another look at the North Atlantic ACE-to-date compared to previous calendar-year values from 1948-2008. The ACE of 44, if the season ended today would be the lowest since 1993, 1994, and 1997 and among the slowest years in the past half-century. Here is a quick listing: LISTING
October 21: Hurricane Neki in the Central Pacific has slowly gained strength and may become the next major tropical cyclone in the Northern Hemsiphere during this rather active October. NH ACE numbers have gained considerably and come off the 30-year lows experienced during the past 2-3 years at various times. The NH ACE of 375 through October 21 puts 2009 ahead of 1981, 1983, and 2007. The 30-year average ACE for the NH is 467 with 50% coming from the Western Pacific. The North Atlantic is still very quiet and it appears that the ACE of 44 will rank as one of the least active years overall. October 19: Northern Hemisphere and Global Tropical Cyclone activity metrics have come off their 30-year lows a bit with extremely powerful Category 5 Rick and SuperTyphoon Lupit. With the ongoing developing El Nino, additional Central Pacific activity like Neki is expected as well as more powerful SuperTyphoons in the Western Pacific.
October 15: With October nearing half over, here is a quick look at the North Atlantic ACE-to-date compared to previous calendar-year values from 1950-2008. The ACE of 44, if the season ended today would be the 13th slowest or weakest since 1950. According to the bar chart, years with less ACE include 1983, 1977, 1982, 1994, 1987, 1991, 1962, 1972, 1986, 1993, 1970, and 1997 -- in respective order beginning with weakest. Here is a quick listing: LISTING
October 11: With the departure of Melor into the midlatitudes, Parma continues to linger on and Nepartak has joined the recent Western Pacific cyclone parade. The burst of ACE has slowed down to a trickle with the Northern Hemisphere total sitting at 320. The average of the past 30-years was 435, so about 74% of "normal". October 5: Long-lived typhoons Parma and Melor will combine for over 60 ACE points this week, which will account for almost one-fifth of the overall 2009 Northern Hemisphere output. Thus, it is important to consider the impact of individual storms on the overall TC energy budget of the hemisphere, especially such large Super Typhoons as Melor. Coincidentally, as the 2009 NH ACE has ticked up to 303 -- the current year-to-date ACE back in 2007 was also rapidly increasing (it was 304). Since the Eastern Pacific and North Atlantic are unlikely to produce much in the way of ACE during the rest of 2009, it is the Western Pacific that will be the place to watch for more tropical cyclones. September 30 - October 3: End of month global update. The Western Pacific is very busy with powerful Typhoon Parma rapidly intensifying to 100 kts+ Major Status. Parma will likely become a SuperTyphoon. The Northern Hemisphere ACE total is 258 through the end of September. This is the lowest value since 1977 for calendar-year-to-date NH ACE and the average is 403 (1979-2008). However, with Parma and Melor at typhoon intensity, it is expected that the NH ACE will catch up a bit as October progresses (no thanks to the North Atlantic, which looks a lot like November out there). September 28: The Western Pacific has become active with 3-systems, one a typhoon, one a tropical storm and one a tropical depression. The latter two are expected to slowly gain strength and become typhoons over the next 3-5 days. Meanwhile, the Eastern Pacific and North Atlantic are very quiet with no active INVESTS or tropical cyclones. A major cold front will chill the continental United States this week. September 25: With the dissipation of weak Eastern Pacific tropical storm Nora, the global tropics are again without a named system. A new depression has formed in the WPAC and an Invest 99L near the Cape Verde Islands of the far eastern Atlantic are the only places with potential for activity.
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24-Month Running Sums of Global Tropical Cyclone Accumulated Cyclone Energy (ACE) Global tropical cyclone activity remains near 30-year + lows Figure: 24-month running sum of tropical cyclone accumulated cyclone energy for the entire globe (top black squares / time series) and the Northern Hemisphere only (bottom green squares / time series). The difference between the two time series is the Southern Hemisphere total. Data is shown from January 1979 - October 29, 2009 mainly because intensity estimates of SH cyclones are often missing in the JTWC best-tracks prior to 1980. See notes. |
2009 Northern Hemisphere Tropical Cyclones
Maximum Wind Speed & ACE per storm
Northern Hemisphere Tropical Storms during Calendar Year 2009 = 54
Northern Hemisphere Hurricanes + during Calendar Year 2009 = 25
The 13 Tropical Cyclones that had an ACE > 10 Account for almost 3/4 of the total Northern Hemisphere ACE. 7 (ACE > 24) account for more than 1/2 of the total NH ACE.
Notes on Data and Methods and citation
This page can be cited as ongoing research related to my dissertation and publications resulting from it.Maue, R. N., 2009: Northern Hemisphere Tropical Cyclone Activity. Geophys. Res. Lett., 36, L05805, doi:10.1029/2008GL035946. Abstract Climatology is based upon the past 30-years of tropical cyclone activity (1979-2008). Historical tropical cyclone tracks are obtained from two sources: National Hurricane Center (NHC) for Eastern Pacific and North Atlantic basins and the Joint Typhoon Warning Center (JTWC) for the Western Pacific, Northern and Southern Indian Oceans, and the South Pacific including the Australian region. Best-track data when cyclones are in an extratropical phase are disregarded, where this is included in the datasets. While there are several other sources of best-track hurricane data for the different basins around the globe, it is not apparent which source of tropical cyclone intensity estimates is the best, most correct, or most consistent throughout the past 30-years. Until that research is completed, it is my policy to use NHC and JTWC data for global tropical cyclone data. I will attempt to use RSMC (Tokyo) and the IBTrACS merged database for comparison purposes in the near future. (Update: June 24, after calculating ACE using the IBTrACS mean intensity, which can include from 1-4 different reporting centers, the differences are negligible. Therefore, it is appropriate to use the NHC+JTWC for global studies on yearly time scales. Naturally differences crop up when examining storm by storm and observation by observation differences. This is a disasterous complication when doing count/frequency studies such as Webster et al. (2005) but is mitigated with accumulated cyclone statistical studies (i.e. Emanuel 2005; Maue 2009).