An Exceptionally Slow-Starting Typhoon Season; 95L Fizzles

By: Jeff Masters and Bob Henson , 4:25PM,GMT on June 24,2016


 

Residents of the Northwest Pacific have enjoyed an unusually late start to the typhoon season this year, despite the fact that ocean temperatures have been running about 1°C (1.8°F) above average. Though there has already been one tropical depression, the basin has yet to see a named storm. Typically, 90% of all Northwest Pacific seasons see their first named storm by May 1 (thanks to Mike Fiorino for this stat.) Four named storms, two typhoons, and one intense typhoon typically occur by June 24; last year, we'd already had three Category 5 typhoons by mid-June!


Figure 1. One of 2015's early-season Category 5 typhoons: Typhoon Maysak as seen from the International Space Station at 2118Z (5:18 pm EDT) on March 31, 2015. Image credit: Terry Virts/NASA/ISS

This year is only the sixth time since 1950 that the first tropical storm of the Northwest Pacific season has occurred after June 1:

1998: July 8 start date
1973: July 1 start date
1983: June 25 start date
2016: June 24 and counting…
1952: June 10 start date
1984: June 9 start date

The four years with the latest start dates—including 2016—all occurred during the transition from strong El Niño conditions to neutral or La Niña conditions later in the year.  The upper-level atmospheric circulation associated with this transition bring conditions which discourage tropical cyclones--sinking air, surface high pressure, and dry conditions--to the typhoon breeding grounds of the Northwest Pacific. Surface pressures over the past month in the waters east of the Philippines extending to the Date Line have been 0.5 - 1.5 mb above average over the past two months (Figure 1). The Friday morning Tropical Weather Discussion for the Northwest Pacific from the Joint Typhoon Warning Center highlighted just one area of low concern, and the GFS and European models showed nothing developing for at least the next five days.


Figure 2. Surface pressures between May 1 - June 22, 2016, in the waters of the Northwest Pacific east of the Philippines (extending to the Date Line) have been 0.5 - 1.5 mb above average. Image credit: NOAA/ESRL.

A slow start usually a harbinger of a quiet typhoon season
This year's slow start to typhoon season is likely a harbinger of a season that will be much below-average in activity. Slow-starting typhoon seasons like 1998, 1973, and 1983 all had total activity that was much below average: the Accumulated Cyclone Energy (ACE) in those years were 152, 220, and 147--well below the average ACE from the past 51 years of 298. The May 7 forecast for the 2016 Northwest Pacific typhoon season made by British private forecasting firm Tropical Storm Risk, Inc. (TSR) called for a below-active season with 22 named storms, 13 Category 1 or stronger typhoons, 6 major Category 3 or stronger typhoons, and an Accumulated Cyclone Energy (ACE) of 217. The long-term averages for the past 51 years are 26 named storms, 16 typhoons, 9 major typhoons, and an ACE of 298. TSR rates their skill level as modest for these late May forecasts--13% to 30% higher than a "no-skill" forecast made using climatology.

Quiet start to year in Northeast Pacific as well
The hurricane season hasn’t exactly been hopping on the eastern side of the Pacific either. We have seen only one named storm anywhere east of the International Date Line in 2016: Hurricane Pali, which hit Category 2 strength in mid-January. Pali was the earliest named storm and earliest hurricane on record in the Central or Eastern Pacific (reliable satellite-based records only go back to 1971). One could argue it was an “overflow” storm from the extremely busy 2015 season rather than a true kickoff to the 2016 season.

Despite the slow start to their core tropical season, it’s still possible that the Central and Eastern Pacific will catch up later in the year. Sea surface temperatures remain slightly above average across most of the region south and southwest of Mexico where Eastern Pacific tropical cyclones tend to develop.  The forecast for the 2016 Eastern Pacific hurricane season, issued on May 6 by Mexico's Servicio Meteorológico Nacional (SMN), predicted 17 named storms, 9 hurricanes, and 4 major hurricanes. This is close to the average numbers (east of 140°W) from 1981 - 2010, which were 15 named storms, 8 hurricanes, and 4 major hurricanes. Similarly, in its outlook issued May 27, NOAA predicted that a near-average season would be the most likely outcome in the Eastern Pacific, with a 70% chance of 13-20 named storms, 6-11 hurricanes, and 3-6 major hurricanes. The 2015 Northeast Pacific hurricane season (east of 140°W) featured 18 named storms, 13 hurricanes, and 9 major hurricanes.

The transition from El Niño to La Niña may have a larger effect on the Central than the Northeast Pacific. About half as many named storms form in the Central Pacific between 120°W and 180°W in a La Niña year, compared to an El Niño year. Hawaii is about three times less likely to be impacted by a tropical cyclone in a La Niña vs. an El Niño year, according to Phil Klotzbach (Colorado State University].


Figure 3. Accumulated cyclone energy (ACE) by year for all tropical cyclones in the Northern Hemisphere from January 16 to June 23. Image credit: Phil Klotzbach.

Northern Hemisphere: off to an extremely slow start
This year’s quietude across the Pacific has led to an exceptionally low amount of accumulated cyclone energy in the Northern Hemisphere for the year to date. The contrast with 2015 couldn’t be starker: as pointed out by Phil Klotzbach, the Northern Hemisphere ACE from January 16 to June 23 was the highest on record in 2015 and the lowest on record in 2016. The low ACE is primarily due to the delayed start of the Northwest Pacific season; that basin accounts for nearly two-thirds of Northern Hemisphere ACE up to this point in a typical year, compared to about 2% coming from the Atlantic. The North Atlantic is at a record-setting pace for named storms, with four already observed to date. However, Tropical Storms Bonnie, Colin, and Danielle were all short-lived systems with peak sustained winds of 50 mph or less. January’s off-season Hurricane Alex produced more ACE than these three storms combined.

Phil Klotzbach’s excellent new website for real-time tropical cyclone statistics has a "Basin Archives" button with historical statistics for those wanting more information.


Figure 4. Latest satellite image of Invest 95L over the Gulf of Mexico.

95L in the Southern Gulf of Mexico a low threat to develop
A tropical disturbance over the southern Gulf of Mexico (Invest 95L) has grown less organized since Thursday, and no longer appears to be a threat to develop into a tropical depression. Satellite loops late Friday morning showed 95L had only a limited amount heavy thunderstorms, which were poorly organized and had no signs of rotation. The Air Force hurricane hunter mission scheduled for Friday was cancelled. 95L is expected to move ashore over Mexico between Veracruz and Tampico on Saturday, bringing heavy rains of 2 - 4". In their 8 am EDT Friday Tropical Weather Outlook, NHC gave 95L 2-day and 5-day development odds of 10%. The next name on the Atlantic list of named storms is Earl, but don't expect it to get used for 95L.

None of our reliable models for tropical cyclone genesis are showing anything developing in the Atlantic through at least June 29.

Have a great weekend, everyone!

Jeff Masters and Bob Henson