Hurricane Arthur and eastern United States Heavy Rainfall

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             Hurricane Arthur and eastern United States Heavy Rainfall
                                                    By
                                            Richard H. Grumm
                                 National Weather Service State College, PA

1. Overview

Hurricane Arthur (Fig. 1) and a deep trough (Fig. 2) over the eastern United States brought heavy
rainfall (Fig. 3) to the East Coast of the United States from 3-5 July 2014. Officially (WIKI;
NHC) Arthur achieved hurricane status on 3 July 310 km south-southwest of coastal North
Carolina and reach the North Carolina Coast around 0100 UTC 4 July (Fig. 1c). The lowest
pressure recorded in the storm was 973 hPa; reached category 2 intensity on the Saffir-Simpson
wind scale; and was a relatively rare deep early season hurricane.

As shown in Figure 1, after exiting the North Carolina coast, the storm remained over the
western Atlantic as it tracked to the northeast. The 12-hour estimated rainfall associated with the
both Arthur and the frontal (Fig. 4) indicated that the initial rainfall from Virginia to New
England was associated with a frontal system (Fig. 5). The strong precipitable water (PW)
gradient ahead of the front resulted in a widespread severe weather event on 3 July (Fig. 6) in
contrast to the dearth of severe weather on 4 July as Hurricane Arthur tracked just off the East
Coast of the United States.

Early season hurricanes and tropical storms can affect the eastern United States. The remnants of
Hurricane Agnes in June 1972 was one of the more memorable storms as it tracked from the
Yucatan into the eastern Gulf and affected the East Coast. In the eastern United States, Agnes
was more remarkable for the rain it brought to the Mid-Atlantic region (Bosart and Dean 1991)
and the circuitous track of the storm.

Tropical which interact with frontal systems; as Arthur did; often have Predecessor Rainfall
Events (PRE: Atallah and Bosart 2003; Galarneau et al 2010; Schumacher et. al. 2011). PREs
typically occur about 1000 km poleward of the parent tropical cyclone and the rainfall typically
occurs 24 to 36 hour in advance of the moisture shield associated with the tropical cyclone. The
PRE can produce heavy rainfall and flooding and if the tropical storm also affects the region, the
double whammy can create a significant flood event. Galarneau et al. (2010:Fig. 6 & Fig. 24)
showed that the PRE is often observed in an enhanced jet entrance region well ahead of the
parent tropical cyclone. Schumacher et al. (2011:Fig 2) showed how the interaction of tropical
storm Erin and a strong 250 hPa jet streak produced a high impact flash flood event in Minnesota
while Erin was tracking through Texas and Oklahoma.

As forecasts of Arthur evolved, the pattern was considered likely to produce a PRE. Based on the
rainfall patterns in Figure 4, there clearly was an area of rainfall from central Pennsylvania into
New England ahead of Arthur that may be considered a PRE. This paper will examine the event,

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highlighting the pattern and forecasts of the rainfall associated with the frontal system which
interacted with Arthur.

2. Methods and data

All rainfall data used in this study were obtained in gridded using the 6-hour Stage-IV data
(NCAR/EOL; Nelson and Seo 2010). The data were plotted in 6, 12, and 24 and to cover the
period of the total event.

The storm reports and plots of storm reports were provided by the Storm Prediction Center
(SPC).

The Climate Forecast System Reanalysis data (Saha et al. 2010) was retrieved from NCAR and
the model data was retrieved from NCEP. All gridded data was plotted using GrADS (Doty et al.
1995).

Backward trajectories were computed using the Air Resources Laboratory website. A site near in
the heavy rainbands near Boston and in the frontal rainbands in the Hudson Valley
(Poughkeepsie) of New York were used to compute backward trajectories on 3 and 4 July 2014.

3. Rainfall and Pattern: To PRE or not to PRE

The larger 500 hPa (Fig. 2) pattern, surface pattern (Fig. 1) and the moisture plume (Fig. 5)
showed the key features included the circulation associated with Arthur and a frontal system.
The high PW values and anomalies with Arthur remained separate from the frontal system (Fig.
5). However, backward trajectories on 3 and 4 July 2014 from a point near Boston, MA and
Poughkeepsie, NY (Fig. 7 & 8) suggest many of the air parcels in the frontal rainbands from
central Pennsylvania and southern New England came from near the circulation associated with
Arthur. These points were selected based on the heavy rainfall areas in the 12-hour accumulation
periods and the event total heavier rain bands. Several other points were examined but not
shown.

In addition to the influx of air parcels from off the southeastern coast of the United States
moving into southern New York and New England on 3 and 4 July 2014, a 250 hPa jet core was
present over New York and New England (Fig. 9). The trough and jet were slow to move out of
the region and the strong 250 hPa wind and southerly wind anomalies persisted over the region
from 0000 UTC 4-5 July 2014 (Fig. 9c-e) before rapidly lifting to the north and east.

The rainfall pattern over the northeast was compared to the 250 hPa isotachs (Fig. 10). These
data implied a strong jet entrance region over the region. The 24 hour accumulated precipitation
ending at 1200 UTC 4 July and the 0600 UTC CFS 250 hPa winds show that the rainfall
occurred in the rear right quadrant of the jet. The convective rains bands on 3 July clearly
contributed to the rainfall but the trajectory analysis and the jet configuration suggest a relatively
good PRE setup over the region. The enhanced frontal rain band in Figure 4d extending from

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eastern Pennsylvania into central New England was clearly removed from the main tropical rain
areas. However this band did not meet the criteria of time as it occurred with 12 hours of the
passage of Arthur to the east. The rainbands over southeastern New England were clearly
associated with the circulation and strong northeasterly winds on the poleward side of Arthur.

4. Forecasts of Arthur

Two aspects of the forecast are explored here; the first was when did the NCEP EFSs provide
guidance on the potential for Arthur (Fig. 11); and how well was the pattern and precipitation
forecast in the Mid-Atlantic and New England forecast (Fig. 12).

The surface cyclone positions showing a storm of the coast of North Carolina at 0000 UTC 4
July first appeared in the NCEP GEFS on forecasts issued on and after 1200 UTC 30 June 2014.
Thus 1200 UTC 30 June is the first panel in Figure 11. Each successive run continued to show a
deeper cyclone and only the 0000 and 1200 UTC cycles are shown. The SREF forecasts at
shorter ranges (Fig. 13) show the cyclone near landfall with pressure anomalies on the order of -
5 to -6σ below normal. These data suggest relatively good forecasts of the cyclone with the
GEFS providing about 3.5 to 4 days of lead-time. The higher resolution GFS and EC forecasts
were not compared here.

The rainfall and heavy rainfall potential associated with stalled front and the cyclone were of
particular interest. First, tropical storms and fronts often produce a good combination for heavy
rainfall and the impact along the coast was on the 4th of July, a day normally associated with
outdoor activities and evening fireworks. The SREF probability of 50mm or more QPF for the 24
hour period ending at 0000 UTC 5 July (Fig. 12) implied the threat for heavy rain along the
immediate coast and into south-central New England. The mean QPF (Fig. 14) showed lighter
rainfall amounts farther inland and shorter range forecasts indicated rainfall along the frontal
boundary (Fig. 15) in the PW field and rain more likely associated with the circulation about
Arthur. Clearly, the SREF did not do particularly well predicting the intense rain area in
southeastern New England.

5. Summary

A slow moving frontal system and the circulation associated with hurricane Arthur (Fig. 1)
produced rain along the East Coast (Fig. 3) of the United States on 3-4 July 2014. Arthur was an
unusually early season hurricane which developed off the coast of Florida. Arthur achieved
hurricane status on 3 July 310 km south-southwest of coastal North Carolina and crossed the
North Carolina Coast around 0100 UTC 4 July (Fig. 1c). Both the NCEP SREF and GEFS did
relatively well (Fig. 11 & 13) predicting Arthur to track across eastern North Carolina.

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There were 2 areas of relatively heavy rainfall during this event. The southern area of heavy rain
was over North Carolina (Fig. 3) and was clearly associated with the circulation associated with
Arthur (Fig. 3 & 4). The other area of heavy rain was in southeastern New England which was
associated with the slow moving frontal system and the circulation associated with Arthur.
Lighter rain was observed farther west on 4 July, associated with the frontal system and moisture
from the southwestern Atlantic.

The frontal system became quasi-stationary from central New England into Pennsylvania. This
led to a region of enhanced frontal rain. This region was also in close proximity to the right rear
quadrant of the 250 hPa jet. The pattern as similar to that often associated with PREs (Atallah
and Bosart 2003; Galarneau et al 2010; Schumacher et. al. 2011). The enhanced rainfall in
Figure 3 from eastern Pennsylvania was clearly associated with the frontal system and moisture
for the southwest Atlantic. The backward trajectories (Fig. 7 & 8) support this hypothesis. The
rainfall amounts, outside of the Hudson Valley and southeastern New England were not overlay
impressive implying perhaps not all PREs result in widespread high impact rainfall events.

The frontal system which moved into the eastern United States on 3 July also produced
widespread severe weather (Fig. 6) and contributed to the overall rainfall over the 3 day period
(Fig. 3). Interestingly there was no reported severe convective weather in the eastern United
States on 4 July. However, news accounts and statements from NWS office suggest strong winds
associated with Arthur downed trees and power lines from coastal North Carolina into the
southern coast of Canada.

The predictability horizon (PH) of this system implied that the NCEP GEFS provided about 3.5
to 4 days of lead-time on both the frontal system and the tropical cyclone development. Shorter
range SREF forecasts (Fig. 13) did relatively well with the track, depth, and potential landfall of
the cyclone over eastern North Carolina. The SREF QPFs also showed concentrated areas of
rainfall with the circulation associated with Arthur and the frontal rain area. But clearly, the
locally higher amounts were under predicted especially over southeastern New England.

The forecast data displayed here we shown in long range to shorter range perspective. The GEFS
was used here as an outlook product for the potential of the tropical storm and frontal system.
The SREF was used for shorter range forecast issues. Ideally, the 16 km EFS should perform
better at shorter ranges than the 55km EFS. The GEFS ability to predict storms of this nature will
likely improve in the 2015 as the horizontal resolution of the model moves below 30 km.

6. Acknowledgements

The Pennsylvania State University for data access. The Storm Prediction Center for access to
storm reports.

7. References

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Atallah, E. H., and L. F. Bosart 2003: Extratropical transition and precipitation distribution of Hurricane
Floyd '99. Mon. Wea. Rev., 131, 1063–1081.

Bosart, L. F., and D. B. Dean, 1991: The Agnes Rainstorm of June 1972: Surface feature evolution
culminating in inland storm redevelopment. Wea. Forecasting, 6, 515–537.

Doty, B. E., and J. L. Kinter III, 1995: Geophysical data and visualization using GrADS. Visualization
Techniques Space and Atmospheric Sciences, E. P. Szuszczewicz and Bredekamp, Eds., NASA, 209–
219.

Galarneau Jr., T. J., L. F. Bosart, and R. S. Schumacher, 2010: Predecessor Rain Events Ahead of
Tropical Cyclones, Mon. Wea. Rev., 138, 3272-3297.

Nelson, B. R., D-J. Seo, D Kim, 2010: Multisensor Precipitation Reanalysis. J. Hydrometeor, 11, 666–
682.

Saha, Suranjana, and Coauthors, 2010: The NCEP Climate Forecast System Reanalysis. Bull. Amer.
Meteor. Soc., 91, 1015–1057.

Schumacher, R. S., T. J. Galarneau, Jr., and L. F. Bosart, 2011: Distant effects of a recurving tropical
cyclone on rainfall in a midlatitude convective system: A high-impact predecessor rain event. Mon. Wea.
Rev., 139, 650-667.

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Figure 1. CFS-R mean sea-level pressure and pressure anomalies in 12 hour increments from a) 0000 UTC 3 July 2014 through f) 1200 UTC 05 July
2014. Contours every 4 hPa anomalies in standard deviations from normal as in the color bar. Return to text.

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Figure 2. As in Figure 1 except for 500 hPa heights (m) and height anomalies in 24 hour increments from a) 0000 UTC 1 July 2014 through f) 0000
UTC 06 July 2014. Contours every 60m. Return to text.

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Figure 3. Stage-IV QPE (mm) for the period from 1200 UTC 3 July 2014 through 1200 UTC 5 July 2014. Shading in mm as in the
color bar to the right. Return to text.

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Figure 4. As in Figure 3 except for total QPE for the 12-hour windows ending at a) 1200 UTC 3 Jul through d) 0000 UTC 5 July 2014. Return to text.

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Figure 5. As in Figure 1 except for precipitable water (mm) and standardized anomalies. Return to text.

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Figure 6. Storm reports by type from the Storm Prediction Center (SPC). Return to text.

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Figure 7. ARL backward trajectories for a point near Boston, MA for the 48 trajectory time ending at (clockwise from top left) 0000 UTC 3 July, `1200
UTC 3 July, 0000 UTC 4 July and 1200 UTC 4 July 2014. Return to text.

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Figure 8. As in Figure 7 except for a point near Poughkeepsie, NY. Return to text.

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Figure 9. As in Figure 2 except for 250 hPa winds and v-wind anomalies in 6-hour increments from a) 0000 UTC 3 July 2014 through f) 1200 UTC
5 July 2014. Return to text.

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Figure 10. The total accumulated precipitation for the period 1200 UTC 3-4 July 2014 and the 250 hPa isotachs from the CFS
at 0600 UTC July 2014. Return to text.

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Figure 11. NCEP GEFS forecast of mean sea level pressure and standardized anomalies of the pressure field valid at 0000 UTC 4 July 2014. Forecasts
initialization times are a) 1200 UTC 30 June, b) 0000 UTC 1 July, c) 1200 UTC 1 July, d) 0000 UTC 2 July, e) 1200 UTC 2 July and f) 0000 UTC 3 July 2014. The
start time was based on the first GEFS cycle to produce a close circulation off the East Coast. Return to text.

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Figure 12. NCEP 16km SREF forecast of 50 mm or more QPF in the 24 hour period ending at 0000 UTC 5 July 2014. SREF initialization times are a)
2100 UTC 2 July, b) 0900 UTC 2 July, c) 0300 UTC 3 July, d) 0900 UTC 3 July, e) 1500 UTC 3 July 2014, and f) 2100 UTC 3 July 2014. Return to text.

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Figure 13. As in Figure 12 except forecast of mean sea level pressure and pressure anomalies value at 0000 UTC 4 July 2014. Return to text.

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Figure 14. As in Figure 12 except for the ensemble mean QPF (shaded) and each members 50mm contour and the thick black line is the
ensemble mean 50 mm contour. Return to text.

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Figure 15. As in Figure 13 except for SREF precipitable water and precipitable water anomalies. Return to text.