*2025 tropical season off to a quiet start across the Northern Hemisphere*

While there was a hurricane (Barbara) for a brief time on Monday in the eastern Pacific Ocean, the Northern Hemisphere as a whole has had a relatively quiet start to the 2025 tropical season. In fact, this was reportedly the latest time for the first hurricane to develop in the Northern Hemisphere since 1993. The western Pacific Ocean has not had a single named system so far this season (that could change in a few days) and that may be the latest time ever for that to take place. Map courtesy NOAA, University of Wisconsin (CIMSS)

Overview

The Northern Hemisphere saw its first hurricane of the season on Monday in the eastern Pacific Ocean, but overall, the 2025 tropical season is off to a relatively quiet start. In fact, there are reports that this is the latest time since 1993 for the first hurricane to develop in the Northern Hemisphere. In addition, the western Pacific Ocean hasn’t seen a named storm so far this tropical season and there are (unconfirmed) reports that this may be the latest time ever for that to take place. In the Atlantic Basin, it is still quite early in the season and there has been no activity so far, but there is the possibility of a tropical system in about a week to ten days or so across the southwestern Gulf of America or northwestern Caribbean Sea.

There are currently two tropical storms on the scene in the eastern Pacific Ocean - Barbara and Cosme - and both will head to colder waters in the near-term. Image courtesy NOAA (GOES-West)

Discussion

The Pacific Ocean is by far the most important in terms of overall impact on global tropical activity due to its size which is so large that it is generally separated into two parts...eastern and western...for meteorologists to monitor activity. The official start to the tropical season in both sections of the Pacific Ocean is May 15th and - like the Atlantic Basin where the season officially begins on June 1st – the tropical season in the world’s largest ocean runs through the end of November. Yesterday, the eastern Pacific Ocean (and Northern Hemisphere as a whole) saw its first hurricane of the season (named “Barbara”) and this system has since weakened into tropical storm status with maximum sustained winds of 60 mph. Right on its heels, there is a second tropical storm named “Cosme” with maximum sustained winds of 70 mph; however, it may have difficulty reaching hurricane status as it edges over colder and colder waters of the Pacific Ocean.

One expert on tropical cyclones, Dr. Philip Klotzbach of Colorado State University, reports that this is the latest time since 1993 for the first hurricane to form in the Northern Hemisphere (Northern Hemisphere includes Atlantic, Pacific, and Indian Oceans). The western Pacific Ocean has yet to see a named tropical system and there can be the development within the next few days that would likely heads towards China. There are (unconfirmed) reports that this may be the latest time ever for the first named system to form in the western Pacific Ocean when, on average, three storms would have normally formed by now (credit Meteorologist Joe Bastardi of Weather Bell Analytics).

The Madden-Julian Oscillation (MJO) tracks a tropical disturbance that propagates eastward on a regular basis across the global tropics. This appears to be headed into a “weak” state in coming days which would suggest little, if any, enhancement of upward motion across the Atlantic Basin during the next couple of weeks. Map courtesy NOAA, ECMWF

One of the key teleconnection indices to monitor this time of year is known as the Madden-Julian Oscillation (MJO). The MJO tracks a tropical disturbance that regularly propagates eastward along the global tropics and depending on its location (or “phase”), it can lead to enhanced upward motion in a particular region and, in turn, a higher probability for tropical activity. Indeed, the MJO is currently in a location or “phase” that enhances upward motion across the eastern Pacific Ocean, and it is likely playing an important role in the formation of these two systems, “Barbara” and “Cosme”.  

Sea surface temperatures will play an important role this summer and fall with respect to global tropical activity. There is a large area of cooler-than-normal water across the equatorial Pacific Ocean and a cooler-than-normal area in the main development region of the tropical Atlantic Ocean…both of which should be inhibiting factors. Map courtesy NOAA, tropicaltidbits.com (horizontal black line indicates the location of the equator)

In terms of potential activity in the Atlantic Basin where the season officially began on June 1st, there is the possibility of a system in about a week or ten days somewhere across the northwestern Caribbean Sea or southwestern Gulf of America (perhaps the Bay of Campeche region). If this were to indeed take place, this tropical system would likely then head west/northwest into eastern Mexico. As far as the MJO is concerned, a week or so ago, it appeared that this tropical disturbance may headed towards a location (or “phase” (8)) that would typically lead to enhanced upward motion somewhere in the Atlantic Basin. However, recent computer forecasts suggest the MJO will weaken into the “null phase” before ever reaching “phase” 8 and likely will not play an important role in the tropical Atlantic in the near-term. We’ll continue to closely monitor the Atlantic Basin tropical scene in coming days...the season is still quite young.  

Meteorologist Paul Dorian
Arcfield
arcfieldweather.com

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