User blog:YE/2015 Pacific hurricane season May outlook

so, good afternoon everybody. Yep, it's that time of month again. With hurricane season underway, it's time for my second hurricane seaosn outlook typically done in late May. My next outlook is set for June, but it could be in July.

El Nino
As of late, El Nino has been intensifying. Although officially according to the Climate Prediction Center, Nino 3+4 weeklies have remained the same at +1.0C for four consecutive weeks, dating back to shortly after my April outlook, satellite data courtesy of Levi Cowan has indicated that over the past few weeks, Nino 3.4 (official one), Nino 3 (around 150Wish), and Nino 1+2 (off South America) have been slowly warming. Having a head start with this Nino starting back in May of last year, but staying very weak until around March, this Nino event is on track with 1997 at this time, and although records this far back are somewhat sketchy, a bit ahead of 1982. The reason this is significant is that 1982 and 1997 are the two stronger and only super El Ninos recorded in the 20th century.

However, lets look deeper than the SST's for a moment. As I explained in my April outlook, Westerly Wind Bursts (WWB's) are crucial in the development of an El Nino. What sparks a WWB? Well, three things. MJo pulses, Kelvin Waves (both which bring westerly winds and enhance TC chances and the monsoon trough), and intense W/CPAC tropical cyclones. Not only did Pam and it's WPAC twin spark a WWB along with the strongest MJO pulse in the history of man kind, the three Category 5 typhoons (Maysak, Noul, and Dolphin) have been essential in sparking much-needed WWB's. In addition, aided by the lack of El Ninos during the previous generation, a large sub-surface pool of warm waters has formed, and is moving eastwards due to the WWB's and causing the thermocline to break down.

On top of the current conditions, model support of this El Nino is through the roof. Almost every year since 2010, both the CFS and ECMWF have shown a Modoki El Nino. However, the bias-corrected CFS has not shown this since 2009, and shows a super El Nino forming in about six weeks. In addition, model support from other models like the CMC, BOM, JMA, and a few others is at an all time high and are somewhat more bullish than last year. In addition, the non-bias corrected CFS and Euro do not show a Modoki like they did last year. Thus, this prospective super El Nino has some legs, and the confidence in such event has increased.

What does this mean for hurricane season?
There is somewhat of a myth that El Nino increases Eastern Pacific Hurricane activity, and that if a super El Nino were to form, 2015 would become the most active on record.

However, one should note that El Nino is not all good. In years where a traditional/strong El Nino is present, this could shorten the season slightly. The reason for this is because El Ninos bring warmer than average SST's to Nino region 1+2. Warm water leads to rising air, which keeps the ITCZ closer to the equator, and when the ITCZ is close to the equator, the Coriolis Effect is too weak to support cyclonic formation. While El Ninos do favor more activity due to lower shear and warmer waters, the period of cyclonic formation is sometimes reduced.

This explains why neutral, weak, or post-El Ninos tend to be the most active in record. 1982 is the exception, but that had to due with the +PDO, and the El Nino event that year itself stayed weak until around July, and that year didn't have the fastest of starts ever. Other than that, the active group of EPAC seasons are as follows: 1992 (second year El Nino, has some similarities to 2015, 2nd year El Nino sorta like 2015. Like 2015, the event started out as a Modoki), 1985 (neutral), 1983 (2nd year El Nino, also like this year, but El Nino was past its peak), 1984 (nuetral), 1978 (sorta 2nd El Nino, but El Nino was long gone by hurricane season), and 1990 (neutral, maybe, just maybe, a bona fide El Nino, but a 1st year one if that).

Weak MJO
One thing that has slowed the progress of the El Nino, aside from the record MJO pulse back in March during Pam, is the weak MJO. MJO has been fairly week for quite some time, and this could decrease convection over the EPAC. However, during El Nino years, MJO is usually strongest over the EPAC, since the unusually warm SST's focus it there. I would not consider this factor a major negative, just pointing it out, and one could even argue that this is positive, since when MJO is not in EPAC-heavy phases 7, 8, and to a lesser extent 1, convective active is not suppressed as much.

Other trends
This past winter, the +PDO has been at record levels. This spring the numbers have come down somewhat, to +1.60 in April. This is still the highest total observed since the last active era, in the 80s and most of the 90s.

In addition, SST's have been at record levels since the start of the year. The January, February, March, and May SST totals are as follows: 23.775  23.811   24.167   25.251. Each total is the highest on record for that particular month. 2014, while had the worst EPAC SST's in the modern era and since 1959, did not see as warm SST's in the winter. A look at the SST's shows a very warm band of 30-33C water you typically see at the peak of the season; however, the SST's are a bit cooler south of Cabo San Lucas and the 26C has yet to reach the Gulf of California. These values, though, are still slightly above average for this time of year.

Wind shear has been below average when there have been no winter time systems present, though it is currently a bit above average due to the passage of a cold front. Vertical instability is also well above average.

Looking ahead, mutli-years in advance
This is year is on track to be the 2nd consecutive El Nino year. Statically speaking, during +PDO eras, although the data we have is extremely limited, the EPAC activity remains at a high level for 1-2 years. For instance, a busy 1978 season concluded a mutli-year warm ENSO event from 1976-78. Most notably, after the end of the 1982-83 El Nino, activity was high into 1984 and 1985. After the end of the El Nino from 1991-92, 1993 continued the same pattern, though you could argue an El Nino formed that year. Even in the +PDO, a major-happy 1998 followed 1997, 2003 saw a respectable storm count and a lot of landfalls, following the moderate El Nino year of 2002-03. 2005 saw 15 arguably 16 storms in spite of insane Atlantic activity stealing all tropical waves, and a record September, that followed the Modoki event of 2004-05.

Land impacts
Typical of strong El Ninos, Hawaii is at high risk this year. SST are slightly above near the island chain, and a bit above normal to the east of it. 1982 and 1957 are two of the four strongest El Nino events in history, and both had major Hawaii hits (Iwa and Nina). Both 1997 and 1982, arguably the two best analogues for 2015, also saw a system hit Central America, the Baja California Peninsula, with 1997 also having a powerful hurricane blast Guerrero (Pauline). As such, both the southern Mexico coast, the Baja California Peninsula, and Hawaii are at high risk this season.

On a slightly different note, 1997 featured a powerful 160 knot hurricane off the coast of Mexico. 2009, a moderate to strong El Nino event, saw Rick, 155 knots. Olivia 82 and Kiko 83, both arguably were Cat 5's and existed during the powerful El Nino of 1982-83, which arguably lasted until 1983. Therefore, it is highly likely that we will see a Category 5 hurricane this season, and we could see as many three, as observed in both 1994 and 2002.

Outlook

 * 22 named storms
 * 10 hurricanes
 * 5 major hurricanes
 * ACE: 154

Analogues
1997, 1982, 1987, 1992, 2014

Conclusion
Confidence in the forecast is higher than it was in April with El Nino fully emerged, w3e can narrow down the possibilities of this season. However, the +PDO and record SST remain a wild card, thus the possibility of a season like no other seen before is not ruled out. If El Nino gets stronger than expect, the numbers in future forecast would have to brought down ever so slightly. If the season wants to be competitive with 1992, it needs to play from ahead, not behind. 1992 really got going by the time late June came around, so we will see how this 2015 behaves. If the above normal vertical instability persists, the ACE, hurricane, and major hurricane count will be higher than listed above.