Hurricane Hunting… A New High and Low For Me

by Ken Kula · Published January 5, 2025

U. S. Air Force Reserve WC-130J and NOAA WP-3D Hurricane Hunters

Story and photos by Ken Kula

Hurricane Milton, which formed early in October, 2024 contained the lowest atmospheric pressure that I’ve ever seen. I was in the air traffic control (ATC) industry for thirty-five years (with the FAA and several contractors) and watched many storms come and go. Hurricanes contain some serious aviation weather hazards, which intrigues me. The lower the air pressure is in a hurricane, it usually means the conditions are more intense… higher winds and seas and lower air pressure (that’s why they’re known as low pressure systems). Let me talk about a few items of interest to me, about the aircraft in which crews investigate these huge storms, and what piece of data they brought back from Hurricane Milton that caught my attention.

53rd Weather Reconnaissance Squadron WC-130J lifts off from Quonset Point, RI.

First, let’s talk about my new low in life, about atmospheric pressure. Hurricane Hunter aircraft often fly into storms and head for their center of circulation. Many times a clear zone forms in the center of circulation, known as the “eye” of the storm and usually the lowest atmospheric pressure dwells here. In my air traffic control dealings, two standards of measurement were relevant, one being much more than the other here in the U. S.. Standard atmospheric air pressure on the earth’s surface on a standard day’s temperature (59 degrees F or 15 degrees C) can be measured in either inches or millibars of mercury. Standard pressure is 29.92 inches of mercury (in Hg), or 1013.2 millibars of mercury (mm Hg). An on-aircraft piece of equipment called an altimeter displays the vertical position of an aircraft based upon air pressure.

In the U. S., Class A airspace begins at 18,000 feet above sea level. When a low pressure system is located in or near your airspace, there are limits to what altitudes can be used, based upon air pressure. Between FL180 (18,000 feet) and FL600 (60,000 feet) standard settings of the altimeter in an aircraft is 29.92 inches (millibars are seldom used in the U. S.), Below Class A airspace (closer to the ground), a local station air pressure is used. The problem is that when pressure is lower than the standard 29.92 value, the normal 1,000 feet of vertical separation between FL180 and 17,000 feet is compressed. Aircraft are higher than those on 29.92 in the flight levels (an old saying is “from low to high [altimeter setting] look out above”), so ATC must compensate for this by not assigning FL180, and the next Lowest Usable Flight Level (LUFL) assignable is FL190. The calculations and theory are rather complicated, but here’s a quick list of assignable altitudes with lower air pressure:

Inches of Mercury LUFL
29.92 or higher FL180
28.92 to 29.91 FL190
27.92 to 28.91 FL200
26.92 to 27.91 FL210
25.92 to 26.91 FL220
24.92 to 25.91 FL230

Hurricane Hunter aircraft measured air pressure many times during Hurricane Milton’s life in the Gulf of Mexico. On October 7th, the lowest daily pressure was 905 mm Hg or 26.71 in Hg. On October 8th; the lowest reading of 902 mm Hg or 26.64 in Hg. On October 9th and the lowest reading was 907 mm Hg, or 26.78 in Hg.

Thus, on Tuesday October 8, 2024, the lowest usable flight level was FL220… the lowest that I’ve ever seen and that took away 4 assignable altitudes from ATC near the storm’s center. Hurricane Milton became a Category 4 hurricane, a very dangerous storm. To put this in perspective, the “Perfect Storm” on Halloween night of 1991 only went down to 972 mm Hg, or 28.70 in Hg making FL200 the lowest assignable flight level.

Interesting tidbits…the record for the lowest pressure ever recorded on earth was taken at Guam in the Pacific on October 12, 1979, when a super typhoon reached 870 mm Hg, or 25.69 in Hg… meaning the LUFL was FL230! On the other hand, once while I controlled airspace in northern Maine, the altimeter settings in a huge high pressure system were above 30.92 in Hg, adding extra room between 17,000 feet and FL180. The FB-111A flight I was controlling would not take my assignment of a block of altitudes between 17,000 feet and FL180, but wanted both aircraft to be on the same altimeter setting, not one on 29.92 and one on 30.92.(that’s another story in another article though).

G-IV

NOAA’s Gulfstream IV operates at altitudes higher than the prop-driven hurricane hunters.

OK, that’s my new “low”, now onto a new “high”. The National Oceanic and Atmospheric Administration (NOAA) has flown a pair of specialized Lockheed WP-3D Hurricane Hunters in support of “hurricane hunting” since 1976. The design of the basic P-3 Orion dates back to the 1950s’ Electra turboprop transport. These “high time” airframes each have over 10,000 airborne hours on their airframes and scores each of different hurricane penetrations. A newer Gulfstream jet works at higher altitudes above a hurricane, above the WP-3’s service ceiling.

Current NOAA WP-3D in its newest color scheme, to be retired by 2030.

During September, 2024 NOAA announced that these WP-3Ds will be retired by the year 2030, replaced with Lockheed WC-130Js.

Keesler AFB – based Air Force Reserve WC-130J Super Hercules.

The WC-130J is a specialized C-130J Super Hercules transport currently flown by the Air Force Reserve’s 53rd Weather Reconnaissance Squadron based at Keesler AFB, Mississippi. A total of 10 aircraft are configured for Hurricane Hunting, modified with air sampling equipment and a dropsonde chute for launching probes into a storm. Interestingly enough, during a 2019 interview a crewmember noted that the airframe is pretty much a stock transport with no modifications, including the composite propeller blades. Some additional on-board equipment like radar and communication gear are obvious differences from military transports, as well as the dropsonde chute.

So there’s my new low (air pressure) and a new high (new airplanes) associated with Hurricane Hunting. Watching weather reports that come from hurricane hunting aircraft satisfies my fascination with unusual weather phenomena, and Hurricane Milton definitely gave me some new food for thought about how the storms can adversely affect ATC.

WC-130H-