A Presentation for Air Liquide By Climate Impact Company May 8, 2018 Tropical cyclones 2018 A Presentation for Air Liquide By Climate Impact Company May 8, 2018

Tropical cyclones 2018 Review of 2017 A busy year…accumulated cyclone energy index = 226. Historic Harvey, Irma and Maria. Climate and verification. 2018 Outlook Seasonal activity/hurricane tracks forecast. Forecast factors. Air Liquide Risk

Tropical Cyclones 2017 17 Tropical Storms 10 Hurricanes 6 Intense Hurricanes 226 Accumulated Cyclone Energy Index

2017 was more active than normal No. of TCs in the warm Atlantic Multi-decadal Oscillation period… Accumulate cyclone energy index in the 1995-2017 +AMO period…

Hurricane harvEy review Harvey track… Harvey historic rainfall…

Hurricane Harvey Risk Exceedance Probabilities 1-in-1000 year risk exceeded in Houston to Port Arthur stretch. 1-in-1000 year risk extended well inland. Well beyond Alison (2001) intensity.

Why Did Harvey Stall Over Texas? Blocking high pressure over northwest North Atlantic to northern Canada. High pressure ridge correlated to warm northern latitude SSTA. Also linked to limited polar ice cap (from preceding winter).

Hurricane Harvey review Maximum water levels… Storm max wind speed history…

HURRicane Irma review Category 5 Hurricane Irma approaching Puerto Rico… Irma historical wind profile…

Hurricane maria review Category 5 Hurricane approaching Puerto Rico… Sea level pressure drop to record low 909 MB (previous 914 Irma) prior to striking Puerto Rico…

Why was season so intense? Rapid descent to low upper shear environment due to La Nina… Plentiful upper ocean heat in tropical North Atlantic…

2017 North atlantic tropical cyclone season by month

2017 forecast vs. verification Climate Impact Co. Forecast… Observed 2017 Tracks/Intensity…

The 2018 North Atlantic Outlook Normally active year, nothing like last year. 12 tropical cyclones, 7 hurricanes and 3 intense hurricanes. ACE index is 93 (226 last year). Key: ENSO trending toward El Nino, upper ocean is cooler.

The 2018 Climate impact co. forecast Seasonal activity forecast and hurricane tracks… 1999-2017 Verification of April 1 forecasts…

Why less activity in 2018 versus 2017? Increasing risk of El Nino (transition opposite of last year)… ECMWF Indicates El Nino, note tropical Atlantic is NOT warm…

Enso history for tropical cyclones Each ENSO phase and typical seasonal activity… Each ENSO phase and accumulated cyclone energy…

Forecast factors for 2018 ENSO: Rather than a rapidly developing favorable SHEAR environment due to an El Nino to La Nina transition last year, the opposite is likely this year. So…Expect increasing upper shear suppressing tropical cyclone development mid-to-late season. Tropical North Atlantic surface (and subsurface) not robust warm, likely averaging near normal…lowers risk of stronger storms. Quasi-biennial oscillation entering negative phase…limited ventilation deep tropics to allow systems to develop (but subtropics are favorable). Gulf of Mexico has cooled recently but is expected to be warmer than normal this season. So…inhibiting factors for development are ESNO, lack of anomalous warmth in the tropical Atlantic and evolving –QBO. Analog years are 2001 and 2006.

What do analog years show? 2001: Most activity east and south of U.S. (Note Allison). 2006: Most activity east and southeast of U.S.

2018 seasonal forecast chart Tropical Storms Hurricanes Intense Hurricanes Accumulated Cyclone Energy 2001 9 4 2 79 2006 15 106 Forecast 12.0 (12) 6.5 (7) 3.0 (3) 92.5 (93) Last year 17 10 6 226 30-year history 13.5 6.9 3.0 114.8 15-year history 15.4 7.4 3.4 123.5 Weak El Nino 11.4 6.6 106.7

2018 industry leaders forecasts Climate Impact Co. Colorado State Univ. T.S. Risk/U.K. 30-year normal Last year Tropical Storms 12 14 13.5 17 Hurricanes 7 6 6.9 10 Intense Hurricanes 3 2 3.0 Accumulated cyclone energy 93 130 84 114 226

Csu u.s. coastal strike risk of at least 1 major hurricane assessment Forecast Probability (CIC) Normal Probability Entire U.S. East Coast 63% (45-50%) 52% U.S. East Coast 39% (30-35%) 31% Gulf of Mexico 38% (25-30%) 30% Caribbean Sea 52% (40-45%) 42%

Air liquide 2018 tropical cyclone coastal risk assessment 1-5 Scale (5 = highest risk) Texas Coast Louisiana Coast Florida Carolinas Mid-Atlantic Risk Major Hurricane 2 2.5 Risk Hurricane 3.5 3 Risk Tropical Storm 4 No storms 1.5 ALERT FORECAST MODERATE HIGH WEAK MODERATE

Air liquid 2018 tropical cyclone season forecast summary 12 tropical storms (13.5 normal) 7 hurricanes (6.9 normal) 3 intense hurricanes (3.0 normal) Accumulated cyclone energy = 93 (114 normal) CIC Activity forecast 12-14 tropical storms 6-7 hurricanes 2-3 intense hurricanes Accumulate cyclone energy = 93-130 Consensus of forecasters Weak La Nina to weak El Nino suppresses risk of a 2017 repeat. Cool to near normal surface/subsurface tropical North Atlantic. -QBO favors strongest activity in subtropics. Factors 2017 was bad! Not expecting a repeat in 2018. Forecast is near normal activity, coastal risk (in Gulf). If ENSO stays neutral and tropical North Atlantic warms 2018 will be more active than forecast (but still not as bad as last year). 2018 storms should be strongest AFTER they depart deep tropics.