Forecaster summary - Issued 2025-06-26T00:17:53

High-energy (≥2 MeV) electron flux observed by GOES-19 has persisted at mainly Moderate, however the onset of the fast winds of CH59 is likely to have a two-fold impact on day 1 (26 Jun). Initially this is likely to compress the outer Van Allen belt inward, leading to the observed flux at GOES to drop to background.  However, the ongoing fast wind and expected geomagnetic activity is then also expected to result in the charge increasing through this belt, but mainly at lower orbits. As the solar wind pressure gradually eases from day 2 (27 Jun), this enhanced flux is expected to expand outwards towards GEO. This is likely to bring Moderate to High later day 2 (27 Jun), and perhaps persistently High flux from day 3 (28 Jun).

The associated fluence is expected to respond accordingly, with a chance of becoming Active day 2 (27 Jun), but otherwise likely to become Active day 3 onward (28-29 Jun). Given the slower onset and also the overall lower geomagnetic impact of this feature compared to the previous rotation, persistence is not the best guide, however MOSWOC REFM has yet to yet to take account for the recent solar wind enhancements, so this is also of limited value at the moment. This leads to some reduced confidence in the overall forecast.