Hurricane Hermine the little Cyclone that...

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Hurricane Hermine the little Cyclone that Could By

Richard H. Grumm National Weather Service State College, PA

1. Overview

Hurricane Hermine proved to be an enduring storm, developing in the Gulf of Mexico in late August 2016 and lingering in the Atlantic until 8 September. The weak surface low was identified in the CFSR at 0000 UTC 29 August (Fig. 1a) and its track in 24 hour increments through 0000 UTC 03 September show that the storm deepened off the West Coast of Florida (Fig. 1e) before it raced across Florida and Georgia into the southwestern Atlantic (Fig. 1F). The storm came ashore in Florida as a category I storm. At its deepest the storm had a pressure about −5σ below normal, quite typical of tropical cyclones (Hart and Grumm 2000).

As the storm tracked across the southeastern United States, it produced strong winds, coastal flooding and heavy rainfall (Fig. 2). The storm created high winds and downed trees across Florida into the Carolinas (WIKI 2016) close to the storm track. The most severe coastal flooding was observed in North Carolina in the outer banks mainly north of Cape Hatteras. The maximum 6-hour rainfall rates in the southeastern United States were over 150 mm in hours which were observed in portions of Florida, southeastern South Carolina, and eastern North Carolina. The maximum 12-hour rates covered a larger area from Florida to North Carolina (Fig. 3). The 24 hour rates were similar to the 12 hour rates and covered the same general regions. The rates were locally quite high but not extraordinary for a tropical cyclone.

As the storm moved off the North Carolina coasts, forecasts of the storm became a serious concern for the Labor Day weekend. Storm track (Fig 4) ended up well south and east of earlier forecasts. The rain, wind, and coastal flooding in the Mid-Atlantic region into southern New England were for the most part a bust. The cyclone and most of the strong gradient associated with the storm remained too far offshore to have significant impact. As the storm moved to the north late on the 5th and 6th (Fig. 4f) it produced rain and strong winds in coastal areas of southeastern Massachusetts. The easterly flow produced strong rip currents along the East Coast. Thus, despite the rain and wind, the closed beaches probably mitigated the loss of life on what is normally a busy Labor Day beach weekend in NJ and LI.

From the Mid-Atlantic region northward, the storm produced little impact in terms of rainfall1. As shown in the 3 day QPE shield ending at 0000 UTC 6 September 2016 (Fig. 5), the storm did

1 There were some reports 6-7 September of over an inch of rain and winds over 40kts in locations such as Nantucket, MA. 2016-09-05 18:29 METAR KACK 052229Z 03028G42KT 1 3/4SM R24/6000VP6000FT -RA BR OVC005 18/18 A2981 RMK AO2 PK WND 03043/2217 RAB18 P0000 T01830178 = 2016-09-06 07:53 METAR KACK 061153Z 10017G23KT 8SM BKN050 21/18 A2995 RMK AO2 SLP142 60000 70125 T02060183 10206 20183 51017 =

https://en.wikipedia.org/wiki/Hurricane_Hermine


not produce significant QPF over the Mid-Atlantic region or southern New England. There were some report of over 1 inch of rain on the Islands around Cape Cod, MA. Rain eventually affected Long Island, after the Labor Day weekend had passed.

This paper will document the storm and show some of the forecast issues. The storm produced heavy rain in the southeastern USA which was well forecast. The storm was not as well forecast above about 35 north and was particularly for locations such as New Jersey, Long Island and southern New England.

2. Methods and Data

The storm positions were obtained from the CFSRV2 using 6 hour data from 24 August through 8 September 2016. These data were plotted using GrADS.

The QPE data was obtained from 6-hour Stage-IV data. These data were examined from 30 August through 8 September 2016. Regional Storm totals (Fig. 2 & 4) were computed using GrADS. The 6-, 12-, and 24-hour rates were computed and plotted using Python and MATPLOTLIB.

Forecast data were from the NCEP GEFS plotted in GrADS.

3. Analysis

The surface cyclone and anomalies were shown in Figure 1 & 4. Hermine was a relatively well defined and deep cyclone from 1 to 5 September 2016. Off the Mid-Atlantic coast the storm weakened and meandered for several days. The 500 hPa pattern (Fig. 6) showed that the storm developed near the southern edge of a weak 500 hPa trough (Fig. 6a) and then moved to the northeast. A strong 500 hPa ridge and close 5940 m contour ridge developed to the west of the storm. The storm was separated from the westerlies and stuck between two larger subtropical ridges with positive height anomalies to its west and south.

Similar to many tropical cyclones, Hermine was in a plume of deep precipitable water (PW) and had a blob of higher PW near the cyclone center (Fig. 7). At times PW values exceed 75mm and were on the order of +4σ above normal. Along with the above normal PW plume, the storm had strong 850 hPa winds (Fig. 8) and at times the u-winds were over 6σ above normal. The strong winds and high PW were relatively well aligned with regions of heavy rainfall and the higher rainfall rates in the southeastern United States (Fig. 2 & 4)

The strong winds moved up the coast with the storm (not shown) as did the plume of high PW air (Fig. 8). However the deep plume of moisture along with the strong winds remained well offshore.

4. Forecasts


The GEFS forecasts of the cyclone and the QPF when the storm was forecast to affect the southeast are shown in Figures 10 & 11. The 6 GEFS surface cyclone forecasts (Fig. 10) showed a stronger cyclone moving faster to the east with shorter forecast length. Shorter range forecasts were the most successful and quite remarkable for a global ensemble forecast system.

The accompanying QPF showed an increased chance of 75 mm or more QPF (Fig. 11) as forecast length decreased. Overall these forecasts were quite skillful in defining the region for potential heavy rainfall when compared to the gridded Stage-IV data in Figure 2.

The forecasts for the storm in the Mid-Atlantic region and northeast initially had the cyclone center and QPF shield suppressed to the south and east. But forecasts issues on and after 0000 UTC 31 August 2016 began to show the track shifted to the west (Fig. 12c). The shift included the QPF shield (Fig. 13c) and the strong easterly flow on the north side of the cyclone (Fig. 14). The strong and anomalous easterly winds along the coast were potential forecast issue. Verification data (not shown) implied that these strong winds remained too far east to affect the regions, though it was a close call for a significant event on a busy weekend.

5. Summary

Hermine developed in the Gulf of Mexico in late August and developed into a category I hurricane before coming ashore in northwest Florida on 2 September 2016. It came ashore with 752 mph winds and gusts of 67 mph. The storm produced heavy rain from Florida to North Carolina. Coastal flooding was observed in North Carolina.

As the storm moved off the North Carolina coast, the strong winds and rains moved offshore with it. Despite forecasts for strong winds, heavy rainfall, and coastal flooding from the Mid-Atlantic region into southern New England, the storm was rather uneventful in that region. The GEFS did show a sharp northern edge to the QPF shield and the strong easterly winds. It was a close call for Long Island and eastern New England. It was a close call from a storm with very strong easterly flow.

The close call in the Mid-Atlantic region and southern New England impacted millions of people on the busy holiday weekend to close out the summer of 2016. The lack of rain, wind, and flooding did not set well in the media and public. However, it was a close storm with considerable uncertainty and public forecast likely convey the uncertainty than threat as best as practical. It could be shown that shorter range models, such as the HRRR could have helped improve forecasts on timescales of 0.5 to 1 days. Storm following models may help with storms of this nature in the near future. But the state of forecasting today likely contributed to the poor public perception.

6. Acknowledgements

7. References


Figure 1. CFSR analysis of mean sea-level pressure (hPa) and pressure anomalies in 24 hour increments from a) 0000 UTC 29 August 2016 through f) 0000 UTC 03 September 2016. Isobars every 4 hPa anomalies as in the color bar. Return to text.


Figure 2. Stage-IV estimated QPE (mm) for the period of 0000 UTC 01 September through 0000 UTC 3 September 2016. Return to text.


Figure 3. Maximum precipitation observed over any 6 and 12 hour period from 0000 UTC 1 September through 1800 UTC 3 September 2016. Data displayed where the maximum value was equal to or greater than 25 mm. Contours every 100 mm. Return to text.


Figure 4. As in Figure 1 except for the 12 hour periods from 1200 UTC 3 to 0000 UTC 6 September 2016. Return to text.


Figure 5. As in Figure 2 except for the Mid-Atlantic Region 0000 UTC 3-6 September 2016. Return to text.


Figure 6. As in Figure 1 except for 500 hPa heights (m) and height anomalies in 24 hour increments from a) 1200 UTC 1 September through f) 1200 UTC 6 September 2016. Return to text.


Figure 7. As in Figure 1 except for PW and PW anomalies in 6-hour increments from a) 1200 UTC 1 September through f) 1800 UTC 2 September 2016. PW every 5 mm. Return to text.


Figure 8. As in Figure 7 except for 850 hPa winds (ms-1) and 850 hPa wind anomalies. Return to text.


Figure 9. As in Figure 7 except for 12-hour increments from 0000 UTC 3 to 1200 UTC 5 September 2016. Return to text.


Figure 10. NCEP GEFS forecasts of mean sea-level pressure (hPa) and pressure anomalies valid at 0000 UTC 1 September 2016 from GEFS initialized at a) 0000 UTC 28 August, b) 0000 UTC 29 August, c) 0000 UTC 30 August, d) 0000 UTC 31 August, e) 1200 UTC 31 August, and f) 0000 UTC 1 September 2016. Return to text.


Figure 11. As in Figure 10 except for the probability of 75 mm or more QPF for the period of 0600 UTC 01 through 0000 UTC 3 September 2016. The thick contour is the mean position of the 75 mm contour. 0600 UTC was the start time to include the 1 September forecasts. Return to text.


Figure 12. As in Figure 10 except valid at 0000 UTC 4 September 2016 from forecasts issued at a) 0000 UTC 29 August, b) 0000 UTC 30 August 2016, c) 0000 UTC 31 August 2016, d) 0000 UTC 01 September, e) 00000 UTC 02 September, and f) 00000 UTC 3 September 2016. Return to text.


Figure 13. As in Figure 9 except for the probability of 25mm or more QPF for the period of 0600 UTC 3 to 0000 UTC 5 September 2016. Return to text.


Figure 14. As in Figure 12 except for 850 hPa wind (ms-1) and u-wind anomalies. Return to text.


ACK observations

016-09-06 21:53 METAR KACK 070153Z 10014G20KT 9SM CLR 20/19 A3005 RMK AO2 SLP177 T02000189 = 2016-09-06 20:53 METAR KACK 070053Z 10014G23KT 9SM CLR 21/19 A3005 RMK AO2 SLP175 T02060189 = 2016-09-06 19:53 METAR KACK 062353Z 10011KT 9SM CLR 20/19 A3005 RMK AO2 SLP175 T02000189 10244 20200 53015 = 2016-09-06 18:53 METAR KACK 062253Z 10013G19KT 8SM CLR 21/19 A3003 RMK AO2 SLP168 T02060189 = 2016-09-06 17:53 METAR KACK 062153Z 10014G23KT 9SM CLR 22/19 A3001 RMK AO2 SLP163 T02170189 = 2016-09-06 16:53 METAR KACK 062053Z 11015KT 9SM CLR 23/19 A3000 RMK AO2 SLP160 T02280189 51003 = 2016-09-06 15:53 METAR KACK 061953Z 10015G25KT 10SM CLR 23/19 A3000 RMK AO2 SLP159 T02330194 = 2016-09-06 15:10 METAR KACK 061910Z 10015G21KT 10SM FEW026 24/19 A3000 RMK AO2 T02390194 = 2016-09-06 14:53 METAR KACK 061853Z 09013G20KT 10SM BKN024 24/19 A3000 RMK AO2 SLP159 T02390194 = 2016-09-06 13:53 METAR KACK 061753Z 09015KT 10SM CLR 24/19 A3000 RMK AO2 SLP157 T02390194 10244 20206 50001 = 2016-09-06 12:53 METAR KACK 061653Z 09015G22KT 10SM CLR 24/20 A3000 RMK AO2 SLP159 T02390200 = 2016-09-06 11:53 METAR KACK 061553Z 10017G24KT 10SM CLR 24/19 A3000 RMK AO2 SLP160 T02390194 = 2016-09-06 10:53 METAR KACK 061453Z 11016KT 9SM CLR 23/19 A2999 RMK AO2 PK WND 12026/1423 SLP156 T02330194 53014 = 2016-09-06 09:53 METAR KACK 061353Z 11018G26KT 9SM CLR 23/19 A2998 RMK AO2 PK WND 09029/1305 SLP151 T02330194 = 2016-09-06 08:53 METAR KACK 061253Z 10018G24KT 8SM BKN049 BKN110 22/19 A2996 RMK AO2 PK WND 11026/1221 SLP145 T02170189 = 2016-09-06 07:53 METAR KACK 061153Z 10017G23KT 8SM BKN050 21/18 A2995 RMK AO2 SLP142 60000 70125 T02060183 10206 20183 51017 = 2016-09-06 06:53 METAR KACK 061053Z 07010KT 7SM SCT040 BKN050 19/18 A2994 RMK AO2 SLP139 T01940178 = 2016-09-06 05:53 METAR KACK 060953Z 09012KT 8SM OVC044 19/18 A2992 RMK AO2 SLP132 T01890178 = 2016-09-06 04:53 METAR KACK 060853Z AUTO 06010G18KT 7SM OVC041 19/18 A2990 RMK AO2 SLP125 60000 T01890178 53000 TSNO = 2016-09-06 04:14 METAR KACK 060814Z AUTO 06012G19KT 7SM FEW009 SCT021 OVC043 19/18 A2990 RMK AO2 T01890178 TSNO = 2016-09-06 03:53 METAR KACK 060753Z AUTO 06011KT 7SM OVC043 19/18 A2989 RMK AO2 SLP122 T01890178 TSNO = 2016-09-06 03:00 METAR KACK 060700Z AUTO 05013KT 8SM SCT014 SCT019 OVC042 19/18 A2990 = 2016-09-06 02:53 METAR KACK 060653Z AUTO 05016KT 8SM SCT015 BKN019 OVC042 19/19 A2990 RMK AO2 RAE0556 SLP124 P0000 T01940189 TSNO = 2016-09-06 01:53 METAR KACK 060553Z AUTO 05013KT 5SM -RA BR OVC019 19/19 A2990 RMK AO2 RAB0455 SLP125 P0001 60007 T01940189 10200 20183 50009 TSNO = 2016-09-06 01:14 METAR KACK 060514Z AUTO 06012G22KT 3SM -RA BR FEW004 SCT018 OVC025 19/19 A2990 RMK AO2 RAB0455 P0001 T01940189 TSNO = 2016-09-06 00:53 METAR KACK 060453Z AUTO 05015G22KT 4SM BR BKN004 BKN019 OVC036 19/19 A2990 RMK AO2 PK WND 06027/0356 RAB0358E37 SLP126 P0003 T01940189 402000167 TSNO = 2016-09-06 00:45 METAR KACK 060445Z AUTO 05016G22KT 4SM BR BKN004 BKN017 OVC036 19/19 A2990 RMK AO2 PK WND 06027/0356 RAB0358E37 P0003 T01940189 TSNO = 2016-09-06 00:39 METAR KACK 060439Z AUTO 05016G23KT 5SM BR SCT006 BKN023 OVC037 19/19 A2990 RMK AO2 PK WND 06027/0356 RAB0358E37 P0003 T01940189 TSNO = 2016-09-06 00:24 METAR KACK 060424Z AUTO 06014G23KT 2SM -RA BR FEW006 BKN024 OVC034 19/19 A2990 RMK AO2 PK WND 06027/0356 RAB0358 P0002 T01940189 TSNO = 2016-09-06 00:16 METAR KACK 060416Z AUTO 06017G26KT 2 1/2SM -RA BR FEW006 SCT022 OVC033 19/19 A2990 RMK AO2 PK WND 06027/0356 RAB0358 P0001 T01940189 TSNO = 2016-09-05 23:53 METAR KACK 060353Z AUTO 07018G27KT 7SM BKN039 OVC050 20/19 A2987 RMK AO2 PK WND 08029/0314 RAB33E42 SLP116 P0000 T02000194 TSNO = 2016-09-05 23:28 METAR KACK 060328Z AUTO 08018G26KT 7SM FEW005 SCT033 BKN070 20/19 A2987 RMK AO2 PK WND 08029/0314 T02000189 TSNO = 2016-09-05 23:13 METAR KACK 060313Z AUTO 08016G25KT 7SM FEW005 BKN022 OVC070 20/19 A2987 RMK AO2 T02000194 TSNO = 2016-09-05 23:06 METAR KACK 060306Z AUTO 08016G24KT 6SM BR SCT005 BKN014 OVC065 20/19 A2987 RMK AO2 T02000189 TSNO = 2016-09-05 22:53 METAR KACK 060253Z AUTO 07015G22KT 5SM BR BKN005 BKN014 OVC060 19/18 A2987 RMK AO2 PK WND 06034/0213 RAB06E15 SLP116 P0000 60003 T01940183 51018 TSNO = 2016-09-05 21:53 METAR KACK 060153Z AUTO 05022G29KT 5SM BR BKN005 OVC012 20/19 A2985 RMK AO2 PK WND 05031/0106 RAB11E42 SLP109 P0001 T02000189 TSNO = 2016-09-05 20:53 METAR KACK 060053Z 05020G31KT 6SM BR OVC005 19/18 A2984 RMK AO2 PK WND 05039/0000 RAE44 SLP106 P0002 T01940183 =

Hurricane Hermine the little Cyclone that...

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