Solar activity increased to moderate levels. Region 672 (N05E33) produced an M4/2n long duration event with multiple flare centers that occurred at 12/0057Z and had an associated Type IV radio sweep, a Type II radio sweep (estimated shock velocity of 800 km/s), and a Tenflare of 2400 sfu. SOHO/LASCO imagery was limited during the period but data indicates that a full halo CME resulted from the M4 x-ray flare and is expected to become geoeffective (see IIB). Region 672 underwent little change during the period in spot area and the region retains a beta-gamma magnetic classification. Region 667 (S11W72) produced a M3/Sn very impulsive event (sympathetic flare from the M4 event based on SXI and Mauna Loa H-alpha data) at 12/0139Z that had an associated Type II radio sweep with an estimated shock velocity of 870 km/s. The M3 flare also appears to have produced a CME that should merge with the previously mentioned CME. This region remains a magnetically simply structured beta group. No new regions were numbered today.

Solar activity is expected to be at low to moderate levels. Region 672 remains capable of producing isolated low level M-class flares, and has a slight chance of producing a major event.

The geomagnetic field was at quiet levels.

The geomagnetic field is expected to be at quiet to unsettled levels on 13 September through much of 14 September. Late on 14 September a shock passage from the long duration M4 flare mentioned in IA is anticipated. Major to severe storming may likely occur following the onset of the shock and dominate the first half of the period on 15 September. Further, a recurrent high speed coronal hole stream is also expected to become geoeffective on 15 September and continue into 16 September. Levels should return to predominantly quiet to unsettled levels late on 16 September.

  Observed       12 Sep 115
  Predicted   13 Sep-15 Sep  110/100/095
  90 Day Mean        12 Sep 112

  Observed Afr/Ap 11 Sep  001/006
  Estimated     Afr/Ap 12 Sep  002/006
  Predicted    Afr/Ap 13 Sep-15 Sep  008/010-010/015-040/050