Hurricane Erin

By Paul Homewood

 

 

https://www.nhc.noaa.gov/archive/2025/al05/al052025.discus.022.shtml

Hurricane Erin has gone into the books as a Cat 5 hurricane, but that is a long way from the full story.

According to the reports from the National Hurricane Center, Erin briefly got to “near 140kts” on Saturday afternoon – Cat 5s are 137 kts and over.

Shortly after, it rapidly weakened as an eyewall replacement cycle took place:

https://rammb-data.cira.colostate.edu/tc_realtime/storm.asp?storm_identifier=al052025

This apparent spike in wind speeds was not spotted by satellites, which peaked at around 130 kts:

 

https://rammb-data.cira.colostate.edu/tc_realtime/products/storms/2025al05/dgtldvor/2025al05_dgtldvor_202508190900.gif

It is now commonplace for hurricane hunter aircraft to spend hours flying inside hurricanes, even far from Florida as Erin was on Saturday. Consequently they are much more likely to spot a short lived spike in just one small area of the eyewall.

Planes are now much more robust with longer range and can stay in the air longer. The WP-3D Orion, for example, has a range of about 3,800 nautical miles and can fly up to 10-12 hours, sufficient for most hurricane missions. The Gulfstream IV-SP has an even longer range of 4200 nautical miles.

Even just a few years ago this would not have been possible. The Gulfstream, for instance, was only introduced in 1996.

Without this sort of virtually continuous observation, Erin’s peak wind speeds would almost certainly not have been recorded.

In 2012, leading US hurricane scientists, Chris Landsea and Andrew Hagen, looked into the consequences of improving observation methods:

 

Abstract

An investigation is conducted to determine how improvements in observing capabilities and technology may have affected scientists’ ability to detect and monitor Saffir–Simpson Hurricane Wind Scale Category 5 hurricanes in the Atlantic Ocean basin during the mid-twentieth century. Previous studies state that there has been an increase in the number of intense hurricanes and attribute this increase to anthropogenic global warming. Other studies claim that the apparent increased hurricane activity is an artifact of better observational capabilities and improved technology for detecting these intense hurricanes. The present study focuses on the 10 most recent Category 5 hurricanes recorded in the Atlantic, from Hurricane Andrew (1992) through Hurricane Felix (2007). These 10 hurricanes are placed into the context of the technology available in the period of 1944–53, the first decade of aircraft reconnaissance. A methodology is created to determine how many of these 10 recent Category 5 hurricanes likely would have been recorded as Category 5 if they had occurred during this period using only the observations that likely would have been available with existing technology and observational networks. Late-1940s and early-1950s best-track intensities are determined for the entire lifetime of these 10 recent Category 5 hurricanes. It is found that likely only 2 of these 10—both Category 5 landfalling hurricanes—would have been recorded as Category 5 hurricanes if they had occurred during the late-1940s period. The results suggest that intensity estimates for extreme tropical cyclones prior to the satellite era are unreliable for trend and variability analysis.

https://journals.ametsoc.org/view/journals/clim/25/13/jcli-d-11-00420.1.xml

In short, they reviewed ten recent Cat 5s, and concluded that only two would have been rated Cat 5 using the technology available in the 1940s. (The two that would have been categorised were both Cat 5 at landfall, so would have been measured by land-based instruments).

Their paper includes this chart, originally published by McAdie et al in 2009:

Note that the first hurricane hunter jets were only introduced in 1996. Previously NOAA relied on the Orion, which is a turbo jet.

On this occasion the peak winds of Erin were measured by an Air Force Reserve Lockheed WC-130J Hercules, which they have only been using since 1999, replacing the older WC-130H. Moreover, the plethora of instruments carried by hurricane hunters now have improved out of all recognition over the years – Doppler, for example, only began to be used in the mid 1990s. SFMR (Stepped Frequency Microwave Radiometer) was not fully deployed until 2008.

Although dropsondes have been in use for longer, they have only been able to provide accurate data since the introduction of GPS, again during the 1990s.

Hagen & Landsea note:

 

Observations of the peak intensity in strong hurricanes were much less common during the late 1940s/early 1950s when compared with recent years because the ability to measure the central pressure and peak winds in major hurricanes was very limited during the late 1940s/early 1950s. A Category 5 designation would be possible if a hurricane made landfall as a Category 5 at or very near a weather station, or if a ship passed through the center while at Category 5 intensity. Aircraft reconnaissance was generally only capable of recording Category 4 conditions at most because of the inability to penetrate intense hurricanes.

The period 1944–1953 was the first decade of routine military aircraft reconnaissance into Atlantic tropical cyclones.  Hagen et al. (2012) explain that the surface and especially the flight-level winds during this decade lack sufficient accuracy and consistency to be given more than a light weight in the reanalysis of the HURDAT intensity. Instead, the reanalysis of intensity relies heavily on aircraft central pressure measurements, when available. Central pressure measurements are converted to maximum wind speeds utilizing the Brown et al. (2006) pressure–wind relationships. Aircraft penetrations (i.e., fly into the eye) were extremely uncommon for major hurricanes from 1944 to 1949 and for Category 4 and 5 hurricanes from 1950 to 1953 because the aircraft were not equipped for the extreme winds and turbulence often experienced in hurricanes of that strength. Instead, circumnavigations would generally be conducted. When penetrations were not performed, central pressures could not be obtained, and the intensity of the hurricane is highly uncertain.

Significantly they also point out that hurricane hunters could only operate during daylight hours in the 1940s and 50s:

Aircraft intensity information was only available during daylight hours during the late 1940s and early 1950s, since penetrations of that era required low-level flights where the pilots could physically see the sea surface.

Hurricane Camille

To put some bones on all of this, let’s take a look at how Hurricane Camille, the second strongest hurricane to hit the US, was tracked back in 1969.

According to the official reports, a hurricane hunter penetrated Camille at 0016 GMT on 17th August, when central pressure of 905mb was recorded. This was about 28 hours before it made landfall in Mississippi.

Yet it was a further 18 hours before the next aircraft penetrated, despite the storm’s proximity to the coast in the Gulf of Mexico. This was to be the last aerial survey, as ground radar provided the information needed for tracking purposes. During these two long gaps, nobody knows whether winds peaked at even higher speeds.

This is in stark contrast to current practice, when the goal seems to be to search out the highest wind speed they can find just for the sake of it.

https://www.weather.gov/mob/camille

 

There is one other observation in the Camille report worth noting:

So we find that Navy aircraft were not allowed into any storm stronger than a weak Cat 4 and that the Air Force radar was not up to the job!

So when the BBC try to convince you that there are more Cat 5 Atlantic hurricanes than in the past, they are being dishonest.