My 2005 Hurricane Season Forecast

[donsutherland1]

Through March, the MEI experienced a substantial rise before backing off significantly in April. At the same time, the QBO reversed its descent and moved narrowly back into positive territory before resuming its decline. This raises the prospects that the QBO could be near its least optimal during the hurricane season. Consequently, based on the latest data, I now believe that the upcoming season will not as active as the 2004 hurricane season:

Named Storms: 11
Hurricanes: 6
Major Hurricanes: 4

The 2005 season has a much greater than normal probability of seeing its first named storm July 1 or later. During the season, I expect 2-4 storms to make U.S. landfall.

4/6 (67%) of upper-air analog seasons have had a major hurricane make U.S. landfall. Therefore, in spite of the diminished tropical activity, U.S. landfall by a major hurricane appears likely. Odds are nearly equally split between western Florida Peninsula/Florida Panhandle/eastern Gulf Coast and the western Gulf Coast/Texas. Recent SOI data also tends to support the idea of a major hurricane making U.S. landfall.

The highest landfall prospect for tropical storms or hurricanes this season appears to be the Florida Panhandle/western Florida Peninsula. Indeed, in the summer forecast, anomalously high precipitation showed up on the Panhandle in a significant number of analogs. The Texas-Mississippi region has the second highest prospect for landfalling tropical storms or hurricanes. Overall, a disproportionate share of tropical storm or hurricane threats will likely extend along the U.S. Gulf Coast. On the East Coast, the South Carolina/North Carolina region has support for a landfalling storm.

Expanded Discussion:

• Hurricane Seasons following Weak El Niño Winters:

Generally such seasons are less active than normal. 5/8 (63%) of such seasons since 1950 had fewer than 10 named storms. The averages for such seasons were: 8.6 named storms; 4.9 hurricanes; 4.1 major hurricanes.

• February-March MEI:

Since 1950, there have been 18 years when the February-March MEI ranged from +0.000 to +0.800. 13/18 (72%) of those years saw the hurricane season produce 10 or more named storms. The mean figure was 11.8. The median figure was 11.5. The most was 19 and the least 6.

Should the MEI average at or above +0.600, the 2005 season odds would overwhelmingly favor a quiet season. Since 1950, 13/14 (93%) of such seasons had 8 or fewer named storms. The lone exception had a positive QBO.

• Prospects of an El Niño during the Summer:

The April ENSO regional data still supports the idea of a neutral ENSO situation during the June-July-August period.

Currently, the temperatures in ENSO Regions 1+2 and 3.4 rank 35th and 14th warmest respectively since regular recordkeeping began in 1950.

If one examines the 15 years with the closest similarities in the April ENSO region anomalies and selects those that also ranked in the top 15 over the latest 3-month period, one comes up with the following years: 1952, 1966, 1970, 1982, 1990, 1991, 1994, 1995, and 2003.

6/9 (67%) of those seasons saw no El Niño during the June-August period. If one just takes the April anomalies into consideration, 7/10 (70%) and 12/15 (80%) of the top 10 and top 15 matches saw no El Niño during the June-August period.

The March 2005 ENSO forecast saw 10/16 (63%) models below El Niño threshold for June-August. Through September-November, 9/17 (53%) remained below El Niño threshold. Consequently, while it appears unlikely that there will be El Niño conditions during the heart of the summer (June-August), the latter part of hurricane season faces the increasing likelihood of seeing El Niño conditions develop.

QBO:

The QBO will likely average negative and be trending downward during the 2005 hurricane season. This factor tends to argue for a less active season than the 2004 season:

QBO during Hurricane Season/Average Number of Named Storms:
-0.01 to -5.00: 8.4 Named Storms
-5.01 to -10.00: 7.4 Named Storms
-10.01 to -15.00: 8.0 Named Storms
-15.01 to -20.00: 9.7 Named Storms

Tropical North Atlantic Index (TNA):

In years when the March-April TNA that averages +0.30 or above, there is a much above normal probability that the first named storm would develop on or after July 1. Since 1950:

• 8/12 (67%) seasons where the March-April TNA averaged +0.30 or above had their first named storm after June 30.
• 4/12 (33%) seasons where the March-April TNA averaged +0.30 or above had their first named storm before July 1.

All four such seasons that also had an MEI that averaged +0.500 or above started after June 30.

Of the remaining 43 seasons:

• 13/43 (30%) saw their first named storm after June 30.
• 30/43 (70%) saw their first named storm before July 1.

With the possibility that a new El Niño might be lurking toward the latter part of a season that followed a weak El Niño winter, the late start could also contribute to a reduced number of named storms.

Seasons following late-winter extreme blocks:

Since 1950, there have been six years in which the NAO bottomed out at –5.500 or below during the February 15-March 15 timeframe: 1951, 1955, 1958, 1962, 1965, and 2001. Much of the data from those seasons offers additional support for the general hurricane ideas noted above.

• 5/6 (83%) seasons saw one or more Category 4 or stronger hurricanes develop; 4/6 (67%) saw a Category 5 hurricane develop.
• 5/6 (83%) saw their first named storm develop late (August 1 or later).

Recent Southern Oscillation Index (SOI) Behavior:

In April, the SOI fell more than 8 points to a monthly value below –8.00. Since 1950 (using the more reliable hurricane season statistics), 9 seasons saw the SOI fall 8 or more points in April and finish the month at or below –6.00. Among that sample, those years with an SOI of +0.00 or above in March (March 2005 finished at +0.2), the following held true:

• 10 or more named storms: 3/5 (60%)
• 2 or more landfalling storms: 5/5 (100%)
• 1 or more major hurricanes making U.S. landfall: 4/5 (80%)

The SOI data strongly supports the earlier noted idea concerning both landfalling activity and the elevated risk of at least one major hurricane making U.S. landfall. The SOI data is less conclusive on overall tropical activity, though the larger pool, which draws upon only the more recent SOI data, seems to support the diminishing risk of high tropical activity per the higher MEI.

Select 1950-2004 Data:

• Average number of named storms: 10.3
• Average number of hurricanes: 6.1
• Average number of major hurricanes: 2.6
• Average number of Category 5 hurricanes: 0.4
• Average number of Category 4 hurricanes: 0.9
• Average number of Category 3 hurricanes: 1.3
• Average number of Category 2 hurricanes: 1.1
• Average number of Category 1 hurricanes: 2.4
• Seasons with one or more major hurricanes making U.S. landfall: 24/55 (44%).
• Seasons with first named storm after June 30: 21/55 (38%)

[vbhoutex]

As always, thoroughly researched and presented in a form we can understand. Thanks Don.

[donsutherland1]

Thanks, Dave. It will be interesting to see how the season unfolds.

[vbhoutex]

It will be most interesting indeed. Your research is always thorough and your thinking soundly based in that research. I find it interesting that you are coming up with "lower" numbers than most seem to be this season since it appears most people who are relatively well versed in the tropics and how they "work" seem to be coming up with an "active" season. I am not at all versed in analogs but I do understand how you use them and why they seem to work so well. I did not use any in my very cursory analysis for this season, but I did lower my numbers just a little since there is so much(or was) question about the Enso regions and whether we will be going into a possible light El Niino later in the season.

[donsutherland1]

Dave,

If this were a QBO+ season, I'd probably be running 1-2 storms higher with my estimate. I'm also thinking ENSO Region 1+2 will probably run somewhat warmer than last seen but not so warm as to suppress the season. Also, if I thought the season would start earlier, I'd probably add another 1-2 storms. So, my numbers are low relative to some others, including Dr. Gray.

[vbhoutex]

Thanks for a little further explanation Don. Your reasoning makes a lot of sense.

I look forward to the season as it starts and we get to discuss further the ins and outs of these systems and what makes them do the things they do.

[donsutherland1]

I am, as well. I'm doing some additional research and hope to see how some of that works out during the season.

[cycloneye]

As always don well done anaylisis and forecast.Now let's see how the season in reallity pans out.

I also am at a low forecast number range 12/7/3 as I see less activity than 2004 due to uncertainty if el nino will develop at the ladder part of the season.

[rainstorm]

great write up

[donsutherland1]

Thanks Luis and Rainstorm. Overall, I believe both Luis' numbers and mine look very good for the upcoming season. Will the Tropics cooperate? The coming months will tell the story.

[MGC]

Don, good forecast. Our numbers are nearly identical with 11 named system. Good luck.....MGC