It is not often you see East Pacific hurricane season forecasts, so I decided to make my own. NOAA is likely going to release their East Pacific hurricane season forecast later today, but most other agencies do not release seasonal forecasts for the East Pacific basin. Last season, the East Pacific basin saw an above-average season with 22 named storms, 13 hurricanes, and 6 major hurricanes, despite a weak La Niña – which typically suppresses the East Pacific basin. The above-average activity was caused by a positive phase of the Pacific Decadal Oscillation (PDO), which despite cooler sea surface temperatures along the equatorial Pacific, sea surface temperatures remained warm in the part of the Pacific where tropical cyclones develop. It also induced upward motion, allowing more Pacific tropical cyclones to fire thunderstorms.

The 2017 Pacific hurricane season has already began, but is yet to see any major activity. The season officially began on May 15, but Tropical Storm Adrian formed 6 days before the season started. Despite initially being forecast to become a hurricane, Adrian quickly dissipated due to upper-level wind shear, and never regenerated. The models have been on and off with cyclogenesis in the 7-10 day period, but they have been inconsistent. I think we could see some East Pacific activity by late June or July – but I do not see anything significant in the short term.

I think that the East Pacific season will likely be at least near average, but probably not significantly above average. There is still a possibility of El Niño to develop – but these chances are decreasing, and a strong event is unlikely. It is looking very possible that ENSO remains neutral this year, and that could keep the Pacific from becoming a “hurricane hotbed” like it has been the past three seasons. In addition, cooler than normal sea surface temperatures have recently been observed off the Pacific coast, and this pattern typically does not favor overly active East Pacific hurricane seasons.  Unlike the past few years, the PDO signal is not overly positive, and right now it is in fact more negative. I am skeptical that these below-normal water temperatures along the Pacific coast will last into the season, but the pattern for the East Pacific does not look quite as conducive for tropical cyclones as it has been recently. The below-normal water temperatures could continue to move southward into the tropical Pacific, and this could suppress development.

I expect the East Pacific season to have near-average activity with 16 named storms, 9 hurricanes and 4 major hurricanes, including Tropical Storm Adrian. This would be the least active Pacific hurricane season since 2011 if my forecast verified. The primary reasoning for me to not forecast an above-average Pacific season is the less positive PDO and the models trending away from El Niño development. Nonetheless, I think a “dead” season in the East Pacific is somewhat unlikely. Here are my probabilities for each season type:

• 30% chance of an above-average season – will likely occur if the PDO turns more positive during the season, along with the development of El Niño.
• 45% chance of a near-average season
• 25% chance of a below-average season – could occur if the PDO remains in its current state or turns more negative, along with the lack of El Niño.

The general trend is that Atlantic and East Pacific hurricane activity are inversely proportional. Inactive Atlantic hurricane seasons are likely to be active in the East Pacific, and vise versa. This is due to the fact that the AMO and PDO are often in opposite phases. However, last year defied this general trend, with both the Atlantic and East Pacific seeing above average activity. This was caused by a rare Modoki La Niña, with both the AMO and PDO remaining positive.

I will be back for a second post later today discussing the seasonal forecasts released by NOAA. Stay tuned – the forecast is usually released during the late morning hours.