=================================== Weekly Space Weather Highlights =================================== Highlights of Solar and Geomagnetic Activity 11 - 17 September 2017 Solar activity was at predominately very low levels through the summary period, interupted by a brief period of low activity on 12 Sep as Region 2680 (N09, L=317, class/area Hsx/140 on 12 Sep) produced a pair of impulsive C-class flares. 11 Sep saw the X-ray background elevated at the C-level due to slow decay from the X8 flare (R3-Strong) observed at 10/1606 UTC. No Earth-directed CMEs were detected during the period. Of note, two halo CMEs were observed on 17 Sep. The first one, a full-halo CME, was first observed in LASCO C2 imagery at 17/1224 UTC, while the second one was a partial-halo CME, first observed in LASCO C2 imagery at 17/1424 UTC. The source region of both CMEs was determined to be from old active Region 2673 (S09, L=119) which is presently on the back side of the solar disk. Old Region 2673 is due to return on 23 Sep. 10 MeV and 100 MeV protons at geosynchronous orbit exceeded their respective event thresholds during the period, both in response to the X8 flare observed on 10 Sep. At 10/1645 UTC, 10 MeV protons exceeded 10 pfu (S1-Minor), reached a maximum of 1,490 pfu (S3-Strong) and decayed below the S1 level at 14/1725 UTC. The 100 MeV proton flux exceeded the 1 pfu level at 10/1625 UTC, reached a maximum of 68 pfu at 10/2215 UTC and ended at 13/0335 UTC. The greater than 2 MeV electron flux at geosynchronous orbit was at moderate levels on 13-14 Sep and high levels on 11-12 and 15-17 Sep. A maximum of 46,263 pfu was observed at 17/1610 UTC. Geomagnetic field activity was a quiet to minor storm levels (G1-Minor) and major storm levels (G2-Moderate) during the summary period. Quiet to unsettled levels were observed on 11 Sep through late on 12 Sep due to waning effects from a negative polarity CH HSS. Late on 12 Sep through midday on 13 Sep, field activity increased to active to minor storm levels (G1-Minor) in response to CME effects from the 10 Sep X8 flare. During this timeframe, total field peaked at 16 nT, the Bz component reached a maximum southward extent of -12 nT and solar wind speed peaked at about 650 km/s. Quiet levels were observed for the remainder of 13 Sep through midday on 14 Sep. From midday on 14 Sep through 17 Sep, field activity was dominated by effects from a recurrent, positive polarity CH HSS. Unsettled to G1-Minor and G2-Moderate levels were observed through 16 Sep with quiet to active levels present on 17 Sep. During this timeframe, total field peaked at near 22 nT, the Bz component reached a maximum southward extent of -18 nT and solar wind speed peaked at about 775 km/s. Forecast of Solar and Geomagnetic Activity 18 September - 14 October 2017 Solar activity is expected to be at predominately very low levels on 18-22 Sep and 08-14 Oct. R1-R2 (Minor-Moderate) levels are expected on 23 Sep-07 Oct due to the return of old Region 2673 (S09, L=119). The greater than 10 MeV protons at geosynchronous orbit are expected to remain at background levels from 18-22 Sep and 08-14 Oct. A chance for an S1-S2 (Minor-Moderate) proton event is possible from 23 Sep-07 Oct in association with significant flare activity after the return of old Region 2673. The greater than 2 MeV electron flux at geosynchronous orbit is expected to be at high levels on 18-22 Sep, 28 Sep-19 Oct and 12-14 Oct due to CH HSS influence. Normal to moderate levels are expected for the remainder of the outlook period. Geomagnetic field activity is expected to be at unsettled to active levels on 18-20 Sep, 24-25 Sep and 30 Sep-02 Oct with G1 (Minor) storm conditions possible on 27-29 Sep and 11-14 Oct due to recurrent CH HSS activity. Mostly quiet conditions are expected for the remainder of the outlook period.