Typhoons, El Nino and the Republic of the Marshall Islands

Editor's Note: To compare across regions of my own personal interest, I am using the common definitions of cyclones in the S Pacific as >34 knots and comparing them to tropical storms-and-typhoons North of the equator (>34 knots). If I use the phrase 'typhoon' without explanation below you can assume I am saying "typhoons and tropical storms" because on its own 'typhoon' implies >64 knots just as 'hurricane' implies >64 knots.

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While trying to understand the various tropical storm regions in the Pacific I kept reading contradictory statements about the Marshall Islands (RMI). The Marshall Islands are North of the equator and thus outside of the S Pacific cyclone best. Of course, that doesn’t mean they are exempt from tropical storms because the RMI is at the edge of the typhoon region. When you talk to cruisers who are going north to avoid the South Pacific cyclone season, they often will describe the Marshall’s, and Majuro (the capital) in particular, as outside of the region because the country is so far east. Further, besides being outside the typhoon belt, many cruisers will also mention that they will not be in the Marshalls during the peak of typhoon season (i.e., the Boreal summer, July-Aug-ish).

While doing my advance reading, I came across a statement in our copy of Jimmy Cornell’s World Cruising Routes that indicated that the most dangerous time for the Marshalls from a typhoon perspective was actually the Boreal winter (Dec-Jan ish). (Note: I recently saw his newest edition in which he changed that statement to August to early April.)

So, given that we have been planning to head to the Marshalls for the South Pacific cyclone season, and given a possible impending El Nino, I was quite interested in whether the Marshalls are hit by typhoons-or-tropical-storms or not (and if so, how frequently and at what time of year), and whether the possible impending El Nino has any effect on the Marshalls and tropical storm activity.

Here is what I found out…if you love data (like me – another woman who likes math), read on. If you want just the punch lines, skim over the bolded sentences.

1) When is the most risky time of year for tropical storms and typhoons in the Marshall Islands?

Having been a data collector in a previous career, I went as directly to the source as I could. An article published by Spennemann and Marschner (1994) collated typhoon data for the Marshall islands. There are many holes in their data set but it was the most complete that I had access to, and as far as I know the most comprehensive available.  Note: It is not completely clear whether they are including tropical storms in their data or only severe tropical storms and typhoons. I took their data and sorted it by month to create the following
:
Marshall Islands Typhoons by Month

These data are fairly clear and support Jimmy Cornell’s statement: Contrary to the rest of the typhoon zone, the highest risk in the Marshall Islands historically speaking has been between November and January with the summer months being the lowest.

Two obvious questions come to mind: 2) Do these data depend on El Nino? And, 3) as the Marshall Islands cover a large region, do these data support the common conception that the southerly portion of the Marshall’s, including Majuro, are safer than the northerly portion.

Spennemann and Marschner (1994) conducted an El Nino analysis and concluded that El Nino increases the risk (almost triples) of a typhoon coming to the Marshalls. Their reported probability of a typhoon in the region are actually .27 in a non-El Nino year (12 out of 34 non-El Niño years) and .71 in an El Nino year (9 out 14 El Niño years). 

Both of these findings were reiterated in the most recent Pacific ENSO Update (2nd Quarter, 2014  Vol. 20, No. 2   ISSUED: June 11, 2014) in which they state “The risk of a strong tropical cyclone in the RMI is almost wholly dependent upon El Niño.  Nearly all typhoons affecting the RMI occur  during El Niño.  The greatest threat is during November through January.  Historical El Niño-related tropical cyclones in the RMI include: the November 1918 Typhoon, Typhoon Zelda (Nov. 1991), Typhoon Axel (Jan. 1992), and Typhoon Paka  (Dec. 1997).

Regarding the north vs south issue, this graph was on the Pacific ENSO site. I’ve highlighted the approximate Marshall Islands grid in red with the red diamond being Majuro’s approximate position (blown up below right).

TC frequency in NWPacific by grid marshalls majuro

The graph covers 50 years of typhoon data ( >35 knots).  If we take the 4 levels of longitude the number of typhoons listed are: 19 between 12.5N and 15N, 24 between 10N and 12.5N, 35 between 7.5N and 10NTC frequency in NWPacific by grid marshalls majuro zoom and 26 between 5N and 7.5N --- or 43/61 split in half north/south. No obvious trend for the southern portion of the Marshalls to be safer, in fact the raw data tilting the opposite direction. When you consider the quadrants east to west you find: 35, 32, 25, 12. If anything, going east inside the Marshalls might be slightly better.

Again using Spennemann and Marschner (1994)’s data I tried to replicate this finding by splitting the Marshall islands at 8N (thus using just N of Majuro as the split) and counting the number of storms they listed as having affected each atoll. 58% were above 8N and 42% were below 8N. In this case the raw data tilt slightly toward the south being safer, but not enough for most boaters to see a huge difference in boat safety.

In neither set of data could I find evidence that there is a substantial difference in tropical storm and typhoon frequency in the southern Marshall Islands as compared with the northern Marshall Islands.

4) Finally, in terms of absolute numbers, how does the Marshall Islands compare to other places people consider going to avoid tropical storms?

gilstrap_graph

Using the capital of Majuro as our main port, over 49 years the 2.5 degree longitude by 2.5 degree latitude quadrant containing Majuro averaged .16 typhoons per year. Comparing this average with other ports, the quadrant containing Majuro saw more tropical storm-and-typhoon activity than cyclones in S Pacific border areas like the Gambiers, French Polynesia (.03 per year average) or even Tahiti, French Polynesia (.11 ), very similar numbers as Suwarrow, Cook Islands ( .14 per year) and Pago Pago, Samoa (.19), but fewer than the more intense cyclonic activity areas such as Noumea, New Caledonia (.56), Vuda Point, Fiji (.5) or Nieafu, Tonga (.28). 

At first glance it may seem difficult to make a direct comparison because although both cyclones in the S Pacific and typhoons in N Pacific occur throughout the year, the typhoon season is more distributed. However, although the typhoon season is generally more distributed, it is relatively concentrated into a single season in the Marshalls, much like cyclones in the S Pacific.

7 comments:

  1. Livia, interesting number crunching. But you mix "tropical cyclone" (thus including sub-hurricane strength systems) with "hurricane" or "typhoon" -- e. g., "tropical cyclone/typhoon activity" - - so it was not always clear to me when comments referred specifically to hurricane-strength systems. David (SV Pelagia)

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    1. How embarrassing and thank you. Both of the data sets I have define typhoon as >34 knots in that region and now, after doing some more reading, I realize that >34 knots (but <64 knots) should be labeled a tropical storm in the NW Pacific.

      I wanted to compare the Marshalls to the S Pacific so I want to use the >34 knots tropical-storm-and-typhoon definition, so I've added a note above.

      Also, I was not able to find good data differentiating between tropical storms and typhoons in the Marshalls - all of the data I have has them lumped together. I've edited the text to try to make that more clear.

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  2. I wouldn't be embarrassed - - seems others have done the original "mixing up". Of course, even 35+ knots isn't much fun without good protection. (So many times we have missed the all-round protection we're used to in BC.)

    I'm especially currently interested in hurricanes/typhoons given this year's rough h-season in the Baja (with Pelagia not far away in Mazatlan).

    Keep enjoying yourselves,
    David

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  3. This is great info Livia, thank you for researching and posting this, very helpful to we in the same position, right now looking for a good path and timeline north to Japan from French Polynesia.

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    1. Thanks Michael! From another researcher-boater I understand that essentially none pf those typhoons reached hurricane force but also that there are more west wind anomalies in El Nino years.

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  4. This chart only goes back as far as 1995 but it has a color coded graphical depiction of the TD, TS, and Cyclones/Hurricanes for all the Oceans including the actual track they took. I thought it might help you some since it clearly shows which are Tropical Storms and which are Cyclones/Hurricanes. AND it defines all storms (North and South) of the Equator using the Saffir-Simpson Scale which defines TD <34 Knots, TS 34-63 Knots, and Cyclones/Hurricanes Category 1-5 at 64 Knots to >135 Knots. Fascinating site for a data geek. It's pretty interesting since you can actually "guess" by looking at each map which years were "El Nino" as the storms advance further North and East during El Nino. Have fun data geeks - this one is facinating. http://weather.unisys.com/hurricane/index.php

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    1. Wonderful! I'm looking forward to playing with this. We're getting our ducks in order for our passage to Australia so it may have to wait until then. Cheers, Livia

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