Hurricane Ava

Hurricane Ava was the earliest forming Category 5 hurricane on record in the East Pacific basin. The storm is also tied with 2006's Hurricane Ioke as the fifth-strongest Pacific hurricane on record. It was the first named storm of the 1973 Pacific hurricane season. Forming in early June, Hurricane Ava eventually reached Category 5 intensity on the Saffir–Simpson hurricane scale, the first Pacific hurricane to do so in June and the earliest ever in a season. Its central pressure made it the most intense known Pacific hurricane at the time. Despite its intensity, Ava stayed at sea without significant impact.

Ava was given the most advanced measurement and reconnaissance available at the time. Recon flights were conducted and meteorological equipment was tested. The hurricane was also photographed from space by satellites and Skylab astronauts.

Meteorological history

On June 2, 1973, a tropical depression formed about south of Salina Cruz, Oaxaca. It started out nearly stationary, and became a tropical storm late on the same day it formed, the first named storm of the 1973 Pacific hurricane season. Ava then slowly moved westwards away from Mexico and became a hurricane on June 3. Ava became a major hurricane on the afternoon of June 5. On the next day, a United States Air Force recon flight measured a wind speed of and a central pressure of . These measurements made Hurricane Ava by far the most intense storm of the season.

At its peak, Ava had winds of . These winds made the storm a Category 5 hurricane on the Saffir–Simpson hurricane scale (SSHS), the highest category on the scale, and the first Category 5 hurricane since the 1959 season. Ava was also a hurricane with windspeeds rapidly increasing the closer to the eye they were measured. Over a distance of , wind speeds increased from , and they increased from over half that distance. The reading of was roughly lower than the ambient environment far from the storm.

After its peak, Ava started weakening on June 7, as it continued its westward path. Its winds were on June 7 and on the next day. It was no longer a major hurricane after its winds fell to on June 9. Later that day it weakened to a tropical storm. Tropical Storm Ava became Tropical Depression Ava on June 11. The system then turned north and dissipated on June 12. Its remnants then became embedded in the trade winds as a tropical wave.

Forecasting and observation

In terms of how well it was forecast, Ava had the largest error of any cyclone during the season. This 14° error five days out was mainly due to its northward turn when it was a weakening depression.

For a few days, Ava was directly underneath Skylab during its first manned mission. Astronauts acquired photographs of the hurricane, which was big enough for Science Pilot Joseph Kerwin to describe it as "an enormous spiral" that was big enough to dominate the view outside the space station's window and prevent anything else from being seen. Astronauts also provided microwave data through Earth Resources Experiment Package sensors. Skylab also used a scatterometer on the system. Unfortunately, Skylab's scatterometer data was harder to use than normal as it was degraded.

Ava was also underneath the NOAA-2 and Nimbus 5 weather satellites. NOAA-2 provided photographs that were used to estimate Ava's maximum windspeeds. Satellite images were useful throughout the cyclone's existence, as did the wind reports of three ships when Ava was a young tropical storm. Nimbus 5 carried an Electrically Scanning Microwave Radiometer and Temperature-Humidity Infrared Radiometer. Both were used to study Ava. The main data provided by the THIR was data indicating cloud temperatures. The ESMR's main data was on rainfall rates, densities, and distributions. The observations also provided confirmation that clouds that are not vertically developed very much can produce tropical rainfall.

Recon aircraft also penetrated Hurricane Ava. It was the first Pacific hurricane penetrated by National Oceanographic and Atmospheric Administration aircraft, but not by aircraft from other agencies. NOAA craft were laden with sensors and measured wave heights reaching with a microwave radar system and a laser altimeter. That was the first time ever that sea conditions in a tropical cyclone had been measured that way. United States Air Force planes measured central pressure, air temperature, and humidity in the eye pressures using dropsondes. The collection of data from both space and the air was done in order to allow comparisons. Collectively, all of this measuring made Hurricane Ava the best-measured northeastern Pacific tropical cyclone at the time.

Impact and records

Hurricane Ava stayed at sea. Consequently, no one was killed and there was no reported damage. However, when it was a recently named tropical storm, Ava did cause sustained winds below gale

HOME


Content is Copyleft
Website design, code, and AI is Copyrighted (c) 2014-2017 by Stephen Payne


Consider donating to Wikimedia



As an Amazon Associate I earn from qualifying purchases