Suitable Great Red Spot transit times
as seen from the Isle of Man:

Date/Time            Altitude
 2 May 2018  0:42    19.5°
 4 May 2018  2:20    16.3°
 4 May 2018 22:11    13.3°
 6 May 2018 23:49    19.3°
 9 May 2018  1:27    18.1°
 9 May 2018 21:18    10.6°
11 May 2018  3:05    10.4°
11 May 2018 22:56    18.4°
14 May 2018  0:34    19.4°
16 May 2018  2:12    13.2°
16 May 2018 22:03    17.0°
18 May 2018 23:41    20.0°
21 May 2018  1:19    15.8°
21 May 2018 21:10    15.1°  Sky Bright
23 May 2018 22:48    20.1°
26 May 2018  0:26    17.9°
28 May 2018 21:56    19.6°
30 May 2018 23:34    19.4° 

Calculated by Guide 9

The above transits are calculated from the GRS
having a longitude (System II) of 288° on
1st April 2018.
Logitude of GRS derived from data at:-
http://jupos.privat.t-online.de/