Data from Miami prior to 1958 is considered to be “very suspect” by the NWS. Before that time, Miami’s temperatures were recorded from atop a series of high-rise buildings in downtown Miami.
From 1958 to 1977, weather records are still considered to be “somewhat suspect”. During this period, temperatures were recorded next to the terminal at the northeast corner of what is now Miami International Airport, and later from a building at the southeast corner.
In 1977, the official weather station was moved three miles further inland to its current location near the west end of the runways at the airport.
The NWS website states why these early readings cannot be relied on:
It must be mentioned that prior to the establishment of the airport site, the location of thermometers on top of tall buildings in downtown Miami made the accuracy of temperature records for the period 1914-1958 very suspect, especially in radiational cooling or inversion situations. Even the airport records, because of proximity to asphalt roads, parking areas, and runways, must be considered somewhat suspect until winter 1977, when instruments were moved near the west end of the runways at Miami International Airport.
Any Miami temperature record then is only going up against 40 years of valid data, according to the NWS. Miami’s official summer temperature since 1977 is also going to be hotter than before that date, since the gauge is now located much further inland.
Even considering this, many of the recent “records” at the Miami Airport aren’t matched by other nearby weather stations, including the July 2017 record. Why the sudden spike at MIA?
One possible explanation may be the construction of the 826-836 intersection. Since 2009, the project has been adding miles of hot asphalt and concrete in close proximity to the weather station, which could be amplifying the heat island effect.
the 826-836 interchange project is a short distance from the weather station: