Moderate geomagnetic storm conditions (NOAA Kp = 6 + ) were observed between 21:00 UTC on May 15 and 00:00 UTC on May 16. Locally, several intervals of minor storm conditions were observed, with K BEL reaching 5. This activity is associated with the arrival of the high-speed solar wind stream from the large, negative polarity transequatorial coronal hole (returning SIDC Coronal Hole 147), which started to cross the central meridian on May 13. Solar wind conditions showed a significant enhancement, with the solar wind speed increasing up to approximately 810 km/s. The interplanetary magnetic field reached up to about 17 nT, while the Bz component reached values down to -11 nT. Active to minor storm conditions may persist over the next 24 hours due to the continuous influence of the high-speed stream and depending on the evolution of the interplanetary magnetic field, particularly the Bz orientation.

Solar flaring activity was low over the past 24 hours, with only C-class flares. The strongest flare was a C9.5 flare (SIDC Flare 7709), peaking at 16:14 UTC on May 15, which was associated with SIDC Sunspot Group 844 (NOAA Active Region 4435, magnetic type beta). There are currently five numbered active regions on the solar disk. SIDC Sunspot Groups 844 and 867 (NOAA Active Regions 4435 and 4438) are the most complex groups with magnetic type beta. SIDC Sunspot Groups 868 and 869 (both magnetic type alpha) have rotated on disk from the east limb. The solar flaring activity is expected to be low over the next 24 hours, with C-class flares very likely and a chance for M-class flares. Two faint Coronal Mass Ejections (SIDC CME 654 and SIDC CME 655) were observed in SOHO/LASCO-C2 imagery on May 15, directed toward the west/northwest. SIDC CME 654 was first observed around 13:48 UTC and was associated with a C6.7 flare peaking at 13:13 UTC from SIDC Sunspot Group 844 (NOAA Active Region 4435), with possibly associated Type II radio emissions detected at 13:44 UTC. SIDC CME 655 was first observed around 16:36 UTC and was associated with a C9.5 flare peaking at 16:14 UTC from the same region, with possibly associated Type II radio emissions detected at 16:16 UTC. As detected and measured by the CACTus tool, both CMEs were relatively narrow and slow, with projected speeds around 340–360 km/s, and are not considered Earth-directed. No other Earth-directed CMEs were observed in the available coronagraph imagery. The greater than 10 MeV proton flux was below the 10 pfu threshold level over the past 24 hours. It is expected to remain below the threshold level over the next 24 hours. The greater than 2 MeV electron flux measured by GOES 18 and GOES 19 was below the 1000 pfu threshold in the last 24 hours. The greater than 2 MeV electron flux is expected to be below the 1000 pfu threshold over the next 24 hours. The 24-hour electron fluence is presently at normal levels and is expected to remain so over the next 24 hours.

Geomagnetic conditions globally reached moderate storm levels between 21:00 UTC on May 15 and 00:00 UTC on May 16 (NOAA Kp 6 +). Locally, several intervals of minor storm conditions were observed, with K BEL reaching 5. Further active to minor storm conditions, with possible isolated intervals of moderate storm conditions, may persist over the next 24 hours due to the continuous influence of the high-speed stream, depending on the evolution of the interplanetary magnetic field, particularly the Bz orientation. Over the past 24 hours, the solar wind parameters (ACE) reflected enhanced solar wind conditions under the influence of the high-speed stream from the large, negative polarity transequatorial coronal hole (returning SIDC Coronal Hole 147). The solar wind speed increased up to approximately 810 km/s. The interplanetary magnetic field reached up to about 17 nT, while the Bz component reached values down to -11 nT. The interplanetary magnetic field angle was mostly in the negative sector. Further enhanced solar wind conditions are expected over the next 24 hours due to the continuous influence of the high-speed stream.