San Juan was studied in the 1980’s by C.E Duchon who published in 1986, "Temperature Trends at San Juan, Puerto Rico, Bull.Amer.Met.Soc. 67, 1370-1377. A downloadable pdf file of this paper is available through BAMS. Click on Print Version for Duchon, Claude E.
My 20th Anniversary Review of Jones et al 1986 explores how San Juan was specifically mentioned in Wood’s 1988 critique of Jones et al 1986. The issue of San Juan was elucidated in the Wigley & Jones reply to Wood 1988 see point (5) in my Table listing the sparring between Wood and Wigley & Jones.
On the Roger Pielke Snr blog January 29, 2006 there is a post; "Do Urban Areas have Larger Long term Temperature Trends than Other Locations?" You can read the Pielke material at their site which refers to a 2005 paper by González in EOS which draws attention to urban effects in San Juan trends.
So it is fascinating that San Juan represents a double peer reviewed example of exactly how UHI affected data impacts on global gridded trends. Jones et al 1986 incorrectly assumed the trend in San Juan was due to a step in 1970 and made a single upward correction at 1969 for 1899 to 1969 data to eliminate what they saw as a step.
In fact the San Juan data has been warmed progressively by the expanding UHI a point well made in the 1986 Duchon paper and no doubt by the 2005 paper by González in EOS. (see Pielke site) Jones et al 1986 should have FIRST eliminated UHI affected data and then applied their homogeniety testing to stations that survived.
How many more peer reviewed papers does it take to get rid of one example of UHI affected trends out of global gridded data that is underpinning efforts to change global economic policy ?