East Pacific Overachieving, Atlantic and Northwest Pacific Underwhelming

We’re still in the early days of 2018 for tropical cyclone formation across the Northern Hemisphere, but so far the balance of power has favored the Eastern Pacific in a big way. The expected arrival of El Niño conditions later this summer and autumn is likely to give a further boost to hurricane generation in the Northeast Pacific, while making it harder for hurricanes to spin up in the Atlantic.

It’s common for the East Pacific to get off to a quicker start to its season than the Atlantic. However, this month has been exceptional. June has already seen four named East Pacific storms with the arrival of Daniel on Sunday, and at least two more named storms are possible this week before the month is out. In reliable East Pacific records dating back to the 1970s, the largest number of named storms during June is five, according to Dr. Phil Klotzbach (Colorado State University). That total was reached in 1984, 1985, 1990, and 2014.

Sea surface temperatures are mostly warmer than average across the main development region of the Northeast Pacific, except for areas just off the Mexican coast where cooler waters were churned up by Category 4 hurricanes Aletta and Bud in mid-June. Activity in the East Pacific is also supported by the Madden-Julian Oscillation, which is currently in an active phase stalled across the region, thus increasing the odds of tropical development over multiple days.

Figure 1. Infrared satellite image from 1345Z (9:45 am EDT) Monday, June 25, 2018, showing the four systems of interest highlighted in the NHC outlook at top. Image credit: NASA/MSFC Earth Science Branch.

An early appearance for the Eastern Pacific’s fourth named storm

Daniel became a tropical storm on Sunday, June 24, three weeks earlier than the climatological July 14 appearance of the Eastern Pacific’s fourth named storm. At 11 am EDT Monday, Daniel was located far out in the Northeast Pacific, more than 500 miles west-southwest of Cabo San Lucas, and posed no threat to land. Top sustained winds were at 40 mph, down from the peak of 45 mph attained on Sunday afternoon.

Although wind shear around Daniel is light—less than 10 knots—the sea surface temperatures (SSTs) beneath Daniel are below the 26°C (79°F) threshold for tropical development, and Daniel is heading north-northwest toward even cooler waters, along with a drier environment aloft. Wind shear will remain very light, and a few showers and thunderstorms continued to bubble around Daniel’s very compact core on Monday morning, but it’s unlikely Daniel will be able to maintain tropical storm strength for more than a few hours before weakening into a remnant low, perhaps as soon as Tuesday.

The next disturbance behind Daniel is quite weak. In its 8 am EDT tropical weather outlook, the NOAA/NWS National Hurricane Center gave this system only a 10% chance of development over the next five days. The most likely outcome is for its moisture to be wrapped into the circulation of the next system in the queue, a broad surface low in a very moist environment located about 500 miles south of the Gulf of Tehuantepec. This second system, dubbed Invest 96E, has only a 20% chance of developing into at least a tropical depression by Wednesday, as wind shear will be on the strong side through midweek, but an 80% chance through Saturday as the shear relaxes atop warm waters around 28°C (82°F).

Hard on the heels of 96E is a strong tropical wave located in the Southwest Caribbean that will cross Central America and emerge later this week. The GFS and European models agree that large-scale conditions will support development of this system, potentially into a significant hurricane by early next week. NHC gives this wave a 60% chance of becoming a tropical depression in the East Pacific by Saturday.

According to Phil Klotzbach, the earliest third major hurricane on record in the East Pacific was Emilia on July 10, 2012, so it’s possible the next system—which would also be named Emilia—could break that record.

Figure 2. Visible image of Super Typhoon Jelawat in the Northwest Pacific at 0412Z (12:12 am EDT) March 30, 2018, as captured by the NASA-NOAA Suomi NPP satellite. Jelawat is the year’s only typhoon thus far. Image credit: NOAA/NASA Goddard Rapid Response Team.

A quiet typhoon season so far in the Northwest Pacific

Along with the Atlantic, the Northwest Pacific has also been on the quiet side, as shown in the statistics for year-to-date tropical cyclone activity compiled by Klotzbach. As of Sunday, June 25, the amount of accumulated cyclone energy (ACE) for the Northwest Pacific was running at 48% of the year-to-date average for the period 1981-2010.

The Northwest Pacific has seen just one hurricane-strength storm this year: Super Typhoon Jelawat in March. However, the region has gone as late as August 26 (in 1998) before getting its second typhoon of the year, so we have a long while to go before that record is within reach.

No imminent appearance for Beryl in the Atlantic expected

The next name on the Atlantic list of storms for 2018 is Beryl, but Monday morning’s 5-Day Tropical Weather Outlookfrom NHC highlighted no areas of concern for the next five days. The 0Z Monday runs of our top three models for forecasting tropical cyclone genesis—the European, UKMET and GFS models—had one of them, the European model, call for development of an Atlantic tropical depression in the coming week. This model has been persistently calling for development late this week off the North Carolina coast, from an area of low pressure expected to move off the coast on Wednesday morning. However, such a development looks dubious, since it has very little support from the European model’s 50 ensemble members—versions of the model run at lower resolution with slightly different initial conditions—a technique used to provide an ensemble of possibilities of what might happen, given the uncertainties. If such a storm did develop—potentially aided by the warm waters of the Gulf Stream off the North Carolina coast—it could brush by Massachusetts’ Cape Cod on Thursday night and affect the Canadian Maritime Provinces on Friday.

The majority of the tropical Atlantic has below-average sea surface temperatures (SSTs), which should act to inhibit June and July early-season tropical cyclone activity. These cool SSTs are due, in large part, to a persistently strong Azores-Bermuda High over the Atlantic. When this high-pressure system is strong, it drives stronger-than-average trade winds over the tropical Atlantic, which acts to cool the waters through increased evaporation and churning up of cooler waters from below. A good measure of the strength of the Azores-Bermuda High in summer is provided by the North Atlantic Oscillation (NAO) index. When this index is positive, like it has been almost continuously since March, the Azores-Bermuda High will be strong, leading to increased trade winds and cooling of the tropical Atlantic waters. The current forecast calls for the NAO index to remain mostly positive into the second week of July.

Dr. Jeff Masters co-wrote this post.

Figure 3. Departure of sea surface temperature (SST) from average for June 25, 2018. Ocean temperatures are above average off the Southeast U.S. Coast, near average over the Gulf of Mexico and Caribbean, and much below average over the tropical Atlantic between Africa and the Lesser Antilles Islands. These cool SSTs should act to inhibit June and July early-season tropical cyclone activity. Image credit: Levi Cowan, tropicaltidbits.com.