Map: Atlantic Sea Surface Temperature Anomaly, September 4, 2017

Irma intensified rapidly between Sept 4 and 5[1], amid Atlantic sea surface temperatures ranging from 0.9°F to 2.25°F (0.5°C to 1.25°C) above average, relative to a 1961-1990 baseline.

(The baseline can be found in the middle of this page.)

Data for September 4, 2017 is available, here, and archival data is available, here.

A description of the analysis is available, here.