Precipitation Pattern across the North Carolina during Hurricane Matthew – Part 2 of 2: Classic Pattern for Enhanced Tropical Cyclone Rainfall across the Carolinas during Matthew

14591759_1088720037844214_3490765990052607790_nHurricane Matthew dumped a swath of 8 to 18 inches of rain across inland portions of eastern North Carolina during the period of 07 October through 09 October 2016. Several locations reported incredible rain amounts including 18.38 inches in Elizabethtown NC, 17.00 inches in Hope Mills NC, 16.71 in White Oak NC, 16.28 in Godwin NC, 15.62 in Fayetteville NC, and 15.56 in Goldsboro NC. Several all-time one day rainfall records were set as noted in the graphic below. The precipitation pattern was notable for several reasons including the fact that an ideal setup for enhanced rainfall associated with a tropical cyclone was in place and would contribute to the record breaking rainfall and subsequent flooding across eastern NC.

hurricanematthewrainfallhistorical

matthew-ani-lotThe animated regional radar reflectivity loop to the right is from 2358 UTC on 06 October through 0258 UTC on 09 October which shows the evolution of the precipitation across the Southeast during Matthew. Note that much of central and eastern North Carolina had more than 12 hours of moderate to heavy rainfall as noted by the 35 dBz reflectivity values (yellow to orange or red shading). In fact, Fayetteville NC reported a consecutive 14 hours and 5 minutes of moderate or heavy rain between 449 am and 653 pm on 08 October 2016.

The issue of enhanced precipitation associated with tropical cyclones (TCs) and the distribution of the heaviest rainfall associated with TCs has been examined in numerous studies including Croke (2006) which looked at 28 tropical cyclones that made landfall or tracked along coastal North Carolina from 1953 to 2004; Atallah, et. al. (2007) which investigated the precipitation distribution associated with landfalling tropical cyclones over the eastern United States; and DeLuca, Bosart, and Keyser (2004) which examined the distribution of precipitation over the Northeast during landfalling and transitioning tropical cyclones.

modelThe Croke (2006) study was conducted as a part of collaborative research between NC State and several Mid-Atlantic National Weather Service offices following the devastating impact of Hurricane Floyd (1999) which was responsible for killing 52 North Carolinians, including 36 from drowning. The goal of that research was to develop a conceptual model to determine the potential of enhanced precipitation due to the interaction of the TC with other meteorological features prior to landfall. This paradigm would give forecasters an indication of the potential for an enhanced precipitation event by identifying features that may exist at different temporal and spatial scales outside of the TC. From this work, a conceptual model for enhanced rain associated with tropical cyclones was developed. A cartoon of the primary features is shown in the image to the right, largely adapted from the Croke (2006) work.

The presence of the following features can create an environment favorable for enhanced precipitation across North Carolina:
1) An upper level trough over the Great Lakes and Ohio Valley
2) Strong upper-level divergence inland and poleward of the TC associated with a northern stream jet streak
3) Strong inland moisture flux prior to landfall
4) A cold air damming wedge of cooler/more stable air with a surface high pressure system centered over the northeast
5) Development of a coastal front
6) Slow to moderate TC translation speed and proximity to the Carolinas

Not surprisingly, the environment around Hurricane Matthew included all of these features to some extent which enhanced the precipitation across the region and lead to widespread record-breaking flooding. We’ll examine a few of these features relating to Matthew in the paragraphs below.

18_padv1) An upper level trough over the Great Lakes and Ohio Valley – the objective analysis from the Storm Prediction Center Mesoscale Analysis Page showed a well-defined mid and upper-level trough and potential vorticity axis in the 400-250 mb layer across the Ohio and Tennessee Valleys at 18 UTC on 08 October. This larger scale feature is often identifiable 48 hours or more prior to landfall. The strength and southward extension of the PV can often be correlated to the heavier rain fall events.

18_300mb2) Strong upper-level divergence inland and poleward of the TC associated with the northern stream jet stream – the objective analysis from the Storm Prediction Center Mesoscale Analysis Page at 18 UTC on 08 October showed a well-defined upper-level trough across the Great Lakes with a jet streak at 300 mb across the eastern Great Lakes. A well-defined region of enhanced upper-level divergence was analyzed over North Carolina, likely increasing vertical ascent and enhancing rainfall.

spc-sect17-06z-tran3) Strong inland moisture flux prior to landfall – the objective analysis from the Storm Prediction Center Mesoscale Analysis Page showed a well-defined region of 850 mb moisture transport early in the morning on 08 October not only near the tropical cyclone center but also extending northward into the eastern and southern portion of North Carolina. This moisture transport analysis is from 06 UTC on 08 October as the heavy rain was poised to build and move into North Carolina.

spc_sect17_18z_bigsfc-small4) A cold air damming wedge with a surface high pressure system centered over the northeast – while not as pronounced as in other TC events, a cooler and more stable air mass became established across the Piedmont of North Carolina on 08 October. The METAR plot from 18 UTC on 08 October shows surface dew points in the mid and upper 60s across the Piedmont while dew points were in the lower to mid 70s across the Coastal Plain. The parent high pressure center was located off the New England coast which resulted in an in-situ cold air damming wedge across North Carolina. The wedge likely enhanced the rain in North Carolinas as warm moist air on the forward side of the storm was lifted up and over the surface based stable layer.

spc-sect17-18z-sfnt5) Development of a coastal front – The establishment of the in-situ cold air damming (CAD) wedge across the Piedmont can lead to the development of a low-level boundary along the eastern perimeter of the CAD region. The objective surface frontogenesis analysis from the Storm Prediction Center Mesoscale Analysis Page from 06 UTC on 08 October showed a region of surface frontogenesis shown in red contours extending northeast of the center of Matthew across eastern North Carolina. The coastal front marked the boundary of the strong easterly to southeasterly surface flow with a cooler north to northeast flow further inland. Several studies have shown that a surface boundary can focus heavy precipitation in a mesoscale band driven by low-level frontogenesis that often develops left and poleward of the storm track with enhanced precipitation falling along or in cold sector of the boundary.

track6) Slow to moderate TC translation speed and proximity to the Carolinas – while these features are rather intuitive, the Croke (2006) research suggests that at times they are not dominant. Other factors, such as synoptic or mesoscale features have proven to compensate for TC’s with less favorable tracks or translation speed. Still, absent of other features, a TC that is moving slower and closer to the North Carolina will have a greater potential for heavier rain across North Carolina than one that is moving faster and is removed from the coast.

The synoptic and mesoscale pattern across the eastern United States prior to and during the time in which Hurricane Matthew impacted North Carolina fit the paradigm for enhanced tropical cyclone precipitation. This event was a classic and efficient heavy rain producer with all of the features for enhanced heavy rain including: a strong upper level jet poleward of the tropical cyclone, an approaching upper trough, strong low-level moisture flux, a cold air damming region across the interior Piedmont, and a strong coastal front. Forecasters recognized the developing pattern during the days leading up to the storms arrival and it was highlighted in an Area Forecast Discussion from the National Weather Service Raleigh, NC which noted:

“.SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/…
As of 345 PM Friday…

…Threat of life threatening flooding increasing across the Sandhills and Coastal Plain of NC as ideal setup for enhanced tropical rain becomes established…

The biggest threat and impact arises from the potential for extremely heavy rain with amounts forecast to exceed 10 inches across the southeastern and eastern portions of the CWA. The setup for tremendous rainfall associated with a non-land falling tropical cyclone are nearly ideal.

The combination of an approaching tropical cyclone with deep tropical moisture, a coastal front and a cold air damming air mass in the Piedmont providing an enhance region of ascent northward of the tropical cyclone and the approach of an upper trough and cold front that will lead to a left of track precipitation distribution should lead to storm total rain amounts that range near a foot…”

References

Atallah, E., L. F. Bosart, and A. Aiyyer, 2007: Precipitation distribution associated with landfalling tropical cyclones over the eastern United States. Mon. Wea. Rev.,135, 2185–2206.

Croke, M. S., M. L. Kaplan, L. Xie, and K. Keeter, 2005: Examining planetary, synoptic, and mesoscale features that enhance precipitation associated with Tropical Cyclones making landfall over North Carolina. Preprints, 21st Conference on Weather Analysis and Forecasting/17th Conference on Numerical Weather Prediction, Washington, DC, Amer. Meteor. Soc.

Croke, M.S. (2006) Examining Planetary, Synoptic and Mesoscale Features that Enhance
Precipitation Associated with Landfalling Tropical Cyclones in North Carolina, Thesis
(M.S.), North Carolina State University.

DeLuca, D. P., L. F. Bosart, and D. Keyser, 2004: The distribution of precipitation over the Northeast accompanying landfalling and transitioning tropical cyclones. 20th Conference on Weather Analysis and Forecasting, Seattle, WA., Amer. Meteor. Soc.

Posted in CIMMSE, Hydrology, TC and Boundary QPF | 1 Comment

Precipitation Pattern across the North Carolina during Hurricane Matthew – Part 1 of 2: Left of Track Precipitation Distribution

14591759_1088720037844214_3490765990052607790_nHurricane Matthew dumped a swath of 8 to 18 inches of rain across inland portions of eastern North Carolina during the period of 07 October through 09 October 2016. Several locations reported incredible rain amounts including 18.38 inches in Elizabethtown NC,  17.00 inches in Hope Mills NC, 16.71 in White Oak NC, 16.28 in Godwin NC, 15.62 in Fayetteville NC, and 15.56 in Goldsboro NC. The precipitation pattern was notable for several reasons, including the fact that the area of heaviest rain in North Carolina was generally located well removed from the coast. The axis of heaviest rain in North Carolina fell near the Interstate 95 corridor as shown in the precipitation image shown above/to the right from the Southeast Regional Climate Center.

matthew-ani-lotThe animated regional radar reflectivity loop to the right is from 2358 UTC on 06 October through 0258 UTC on 09 October which shows the evolution of the precipitation across the Southeast during Matthew. Note how very little precipitation is occurring east of the storm track as the system moves near the South and North Carolina coast. During most of the time the tropical cyclone impacted North Carolina, the storm had a Left of Track (LOT) precipitation distribution that favored the heaviest rainfall across inland locations in NC. This was not a surprise as two related conceptual models supported this pattern, including the LOT model from Atallah et al. (2007) and the expectation that Matthew would be undergoing extratropical transition (ET) as it approached the Carolinas.

atallah-lot-figureThe Atallah et al. (2007) composite argues that storms that have most of their rainfall distributed on the west side of storm’s track interact with an upper level trough and potential vorticity maximum in a synergistic way. A LOT precipitation distribution is often characterized by a positively tilted mid-latitude trough approaching the tropical cyclone from the northwest. The precipitation stretches out well north of the system. The trough often transitions from a positive to a negative tilt during its interaction with tropical cyclone. Some notable tropical cyclones in the Carolinas with a left of track precipitation distribution include Alberto (2006), and Floyd (1999).

18_padvThe objective analysis from the Storm Prediction Center Mesoscale Analysis Page showed a well defined upper-level trough and potential vorticity axis across the Ohio and Tennessee Valleys at 18 UTC on 08 October in the 400-250 mb layer. This pattern is consistent with the conceptual model presented by Atallah et al. (2007).

Similarly, Extratropical Transition (ET) has been shown to impact the distribution of precipitation of tropical cyclones where the precipitation area expands poleward of the center and the heaviest precipitation is shifted to the left of the tropical cyclone track. ET is a gradual process in which a warm-core tropical cyclone loses tropical characteristics and become more extratropical in nature (Jones et al. 2003).

The cyclone phase space diagram developed by Hart (2003) provides a mechanism to objectively determine whether a system is warm or cold core and whether the thermal structure will promote asymmetry. The diagram describes the evolution of a cyclone including tropical, extratropical, subtropical, and hybrid structures, and provides a way to visualize the location of the cyclone in the continuum between tropical and extratropical. In the cyclone phase space diagram, ET is identified when the system moves from symmetric/warm-core to asymmetric cold-core. For Hurricane Matthew, this occurred from 07 to 09 October as the storm moved from off the Florida and Georgina coasts to near and along the North Carolina coast.

matthew2016-a-gfs-50There are two cyclone phase space diagrams produced by the Cyclone Phase Evolution: Analyses & Forecasts web page for Hurricane Matthew. The cyclone phase space diagram A, which shows thermal asymmetry versus lower-tropospheric thermal wind, produced from the GFS model, is shown above and to the right (click to enlarge). The diagram shows that Matthew evolved from a symmetric warm-core system to an asymmetric warm-core system on the 7th and 8th of October. The National Hurricane Center (NHC) Matthew Discussion from 11am EDT 08 October  noted that “The cloud pattern associated with Matthew is beginning to acquire some extratropical characteristics. The wind field is expanding, and the area of heavy rains is now northwest of the center.”

matthew2016-b-gfs-50In addition, the cyclone phase space diagram B, which shows upper vs. lower-tropospheric thermal wind, produced from the GFS model, is shown above and to the right (click to enlarge). This diagram shows that Matthew evolved from a deep warm-core system to a more shallow warm-core system on the 8th and 9th of October. The  NHC Matthew Discussion from 11pm EDT 08 October stated that “Matthew is undergoing extratropical transition, and there is barely enough convection near the center to keep the system classified as a hurricane…”

Forecasters used these conceptual models during the days leading up to Hurricane Matthew to assess the flooding threat, weigh confidence in the NWP, and localize precipitation guidance from the WPC. The left of track precipitation distribution was noted in an Area Forecast Discussion from the National Weather Service Raleigh, NC which noted

“…the approach of an upper trough and cold front that will lead to a left of track precipitation distribution should lead to storm total rain amounts that range near a foot…”

 

References

Atallah, E., L. F. Bosart, and A. Aiyyer 2007: Precipitation Distribution Associated with Landfalling Tropical Cyclones over the Eastern United States. Mon. Wea. Rev., 135, 2185-2206.

Atallah, E and L. F. Bosart, 2003: Extratropical transition and precipitation distribution: A case study of Floyd (1999). , 131, 1063-1081. Brennan, M. and R. Knabb, 2008: Extratropical and Subtropical Cyclones: NHC Operational Challenges and Forecast Tools.

Hart, R.E., 2003: A cyclone phase space derived from thermal wind and thermal asymmetry. Mon. Wea. Rev., 131, 585-616.

Jones, S.C., P.A. Harr, J. Abraham, L.F. Bosart, P.J. Bowyer, J.L. Evans, D.E. Hanley, B.N. Hanstrum, R.E. Hart, F. Lalaurette, M.R. Sinclair, R.K. Smith, and C. Thorncroft, 2003: The Extratropical Transition of Tropical Cyclones: Forecast Challenges, Current Understanding, and Future Directions. Wea. Forecasting, 18, 1052–1092.

Posted in CIMMSE, Hydrology | Leave a comment

Tropical Storm Hermine Follow Up with Lessons Learned, Wind Gusts and Gust Factors

tcm-wind-11am-0901

Four quadrant wind radii from the raw TCM guidance from the National Hurricane Center for Hermine issued at 11 AM EDT 01 September 2016.

To evaluate the performance of CSTAR related research to operations activities, members of the CSTAR Tropical Cyclone (TC) wind team recently discussed experiences with Tropical Storm Hermine (September 2016).  In addition, the sustained winds, wind gusts, and gust factors for Tropical Storm Hermine were examined across coastal and eastern Georgia, South Carolina, North Carolina and Virginia.

A conference call was conducted with team members from NWS offices in Charleston, Columbia, Newport, Raleigh, Wakefield, and Wilmington along with NWS Eastern Region SSD to examine the event in greater detail and to identify ways to improve the process over both the near and longer term. Hermine had some special circumstances that made the use of the TCM wind guidance more difficult than normal, including the TC’s weak intensity, the limited wind radii on the western semi-circle of the storm, and the fact that the storm was undergoing extratropical transition as it began to exit the region. The CSTAR TCM wind technique likely won’t be able to completely mitigate these issues. However, a couple of other issues were noted and some solutions are being developed to handle these items:
1)    Adjustments are being made to the CSTAR_Wind_from_WindReductionFactor smart tool so that the wind reduction is only applied to winds of 34 kts or greater (inside the TCM envelope).
2)    CSTAR TCM wind technique offices will explore the use of brief conference calls following the NHC coordination call, to discuss the PREAT guidance and ensure offices are using the technique appropriately and are well collaborated.

NWS Raleigh volunteer Victoria Oliva, examined the sustained winds, wind gusts, and gust factors for Hermine across coastal and eastern Georgia, South Carolina, North Carolina and Virginia. Hourly observations of winds and wind gusts from 48 regular ASOS or AWOS METAR locations impacted by the over land wind field associated with Tropical Storm Hermine were examined. The locations examined in this analysis extended from KSAV (Savanah, Georgia) northeast along and just inland of the coast to KWAL (Wallops Island, Virginia). The map below is a subjective analysis of the maximum wind gusts observed during Tropical Storm Hermine across North Carolina.

windgust-20160903

Subjective analysis of the maximum wind gusts (MPH) observed across North Carolina from 02 September to 03 September 2016 during Tropical Storm Hermine.

Only observations from routine hourly METARs were used (special observations and observations not at the top of the hour were excluded). In addition, gust factors were only calculated for sustained winds of 10 MPH or greater. For each observation, the hourly wind gust factor was computed. The gust factor is defined as the ratio between the wind gust of a specific duration to the mean (sustained) wind speed for a period of time.  A total of 860 gust factors were computed for Hermine.

In general, Hermine was characterized by modest sustained winds as it moved across the region although the strength of the wind gusts increased as the storm evolved during extratropical transition as it moved across North Carolina and off the coast. The maximum sustained wind contained in the Hermine data set was only 44 MPH and the maximum wind gust was only 62 MPH. The data set contained a large number of lower end sustained winds and wind gusts. Nearly 82% or 705 out of the 860 observations, contained in this data-set had sustained winds less than 25 MPH.  Only 64 observations, or less than 8% of all observations, had sustained winds of 30 MPH or more and only 3 observations had sustained winds of 40 MPH or more.

hermine-gust-factor-scatter

Scatter plot of sustained winds and gust factors for Tropical Storm Hermine for 48 METAR locations across coastal and eastern Georgia, South Carolina, North Carolina and Virginia

The chart to the right is a scatter plot of the sustained winds in MPH versus gust factors for the 860 observations included in the study along with a best fit regression curve (y = -0.375ln(x) + 2.6175). In general, the chart demonstrates an inverse relationship between the wind speed and gust factor. Not surprisingly, the gust factors with Hermine were rather variable at low sustained wind speeds and generally converged and decreased with increasing sustained wind speed. This chart is very similar to the database of 15 storms used to develop the CSTAR TCM wind technique.

hermine-gust-factor-bins

Histogram of gust factors from Tropical Storm Hermine for 48 METAR locations across coastal and eastern Georgia, South Carolina, North Carolina and Virginia.

A histogram of the frequency of gust factors for Hermine is shown to the right.  The average gust factor for Hermine was 1.58 which is somewhat higher than the average of 1.53 for the database of 15 tropical cyclones used to develop the CSTAR TC wind technique. The histogram data noted that the gust factors were most frequently noted in both of the bins between 1.4 and 1.5 as well as 1.5 and 1.6. Given Hermine’s relatively weak winds, it’s not surprising that the distribution of gust factors for Hermine is shifted to the right when compared to the 15 storm database, while the overall pattern and character of the distribution for Hermine is very similar to the 15 storm study.

hermine-regression-compare

Comparison of gust factor regression equations associated with Tropical Storm Hermine and the 15 storm database used to develop the CSTAR TCM wind technique.

We generated a regression equation using the gust factor data set associated with Tropical Storm Hermine and compared it to the regression equation used in the 15 storm database used to develop the CSTAR TCM wind technique. The figure above  compares the Hermine regression equation to the 15 storm equation. They show a similar trend and generally match each other well, but given the modest wind speeds with Hermine, it’s not surprising that the Hermine curve is steeper than the larger dataset.

To summarize, participants from the six WFOs using the CSTAR TCM Wind technique discussed the techniques performance during Tropical Storm Hermine, and while the feedback received noted that the process seemed to work well and forecasts were generally accurate and well collaborated, some issues were identified. Adjustments to the CSTAR_Wind_from_WindReductionFactor smart tool are being made so that the wind reduction is only applied to winds of 34 kts or greater.  In addition, CSTAR TCM wind technique offices will try to use brief conference calls to discuss the PREAT guidance and ensure offices are using the technique appropriately and are well collaborated. Finally, despite the modest strength of the tropical storm and its extratropical transition as it exited the region, the observed gust factors matched the 15 storm database used to develop the CSTAR TCM wind technique reasonably well and the tools provided good guidance.

 

Posted in CSTAR, TC Inland and Marine Winds, Uncategorized | Leave a comment

HSLC/SHERB Presentation to NWS Central Region Southeast SOO Group

On August 31st, 2016, I was invited to attend and speak at the NWS Central Region (CR) Southeast SOO Group Meeting at WFO Indianapolis on the topic of our (WFO ILN — Wilmington, OH) experiences/research with non-supercell HSLC tornadoes and the use of the SHERB parameter in our operations to help diagnose environments more prone to producing HSLC tornado and damaging wind events.  The CR Southeast SOO Group consists of SOOs from the following offices in Central Region:

  • Indianapolis
  • Jackson (KY)
  • Louisville
  • Lincoln (IL)
  • Paducah
  • St. Louis
  • Springfield (MO)
  • Kansas City

Before diving into SHERB and environment awareness, I wanted the group to see some of the radar-based research that has been done here at WFO ILN by one of our meteorologists, Andy Hatzos.  Andy has taken  this research to the Ohio State Severe Weather Symposium and the 2016 NWA Annual Meeting.  I presented about half of Andy’s slide deck to the SOOs showing some of the rotational velocities, reflectivity characteristics, and other commonalities and challenges we see in the Ohio Valley, particularly during the cool season. Much of Andy’s work focuses on the use of FAA (TDWR) radar and some of the benefits and challenges of this data.  This slide deck is available here in PDF format.  This slide deck — and the challenges/questions it brings — is important to understand in context of what makes research like SHERB so important. The more situationally aware a meteorologist is to environments that can produce HSLC tornado and damaging wind events, the more effective the messaging will be in all formats — including social media, outlooks, decision-support briefings, and most importantly, warnings.

Andy’s presentation was an excellent segue into the importance of SHERB use in operations. Graciously, Keith Sherburn provided me a wealth of background slides on SHERB development and verification, to which I added some brief case events from the WFO ILN area.  The slide deck I put together from several of Keith’s presentations is available here in PDF format.

The presentations were well received with good dialog and discussion – and I was thrilled to be able to present and discuss SHERB use outside the CSTAR footprint where it was developed.  A hearty thank you to Keith and Andy for allowing me the opportunity to present their outstanding work.      — Seth Binau (WFO ILN SOO)

Posted in Convection, High Shear Low Cape Severe Wx | Leave a comment

Forecasts of Winds and Wind Gusts Associated with Tropical Cyclone Hermine Using CSTAR Research

The approach of Tropical Cyclone (TC) Hermine provides WFOs in the Carolinas and Virginia with another opportunity to use and evaluate a technique to forecast tropical cyclone winds and wind gusts. A Collaborative Science, Technology, and Applied Research (CSTAR) project with North Carolina State University and over a half dozen WFOs in the Southeast, examined ways to add science and to improve inland wind and wind gust forecasts associated with TCs. The CSTAR TC wind technique consists of three primary improvements including a bias correction of the TCM wind vortex, using collaborated wind reductions over land, and using collaborated wind gust factors for wind gust grids across the domain.

tcm.wind.11am.0901

One of the primary difficulties forecasters at the local Weather Forecast Office (WFO) experience during TCs is with forecasting wind and wind gusts. This largely originates from the need to downscale the limited spatial and temporal resolution of the guidance provided by the National Hurricane Center (NHC) to the 2.5km resolution gridded forecast that the local WFOs create for the NDFD. The image to the right is a plot of the guidance provided by the NHC that includes wind radii for the four quadrants of the storm for 34kt, 50kt, and 64kt winds. This forecast for Hermine is from 15 UTC on 01 September, 2016 and is derived from the NHC TCM wind product.

The CSTAR TC wind methodology was utilized by several WFOs in the Southeast beginning as early as Tuesday. The new methodology is used in the Gridded Forecast Editor (GFE) and uses two new forecast grids: the Wind Reduction Factor and the Wind Gust Factor. By providing forecasters with the opportunity to vary these two grids both spatially and temporally across the forecast area and allowing the values to be collaborated across WFO boundaries and maintained from shift to shift, improved forecasts are expected. An example of the Wind Reduction Factor (left) and Wind Gust Factor (right) grids used during Hermine at 20 UTC on 31 August, 2016 valid at 02 or 03 UTC on 03 September, 2016 is shown below.hermine.reduction.factor.gust.factor.4pm.0831

Despite some initial technical and procedural issues , the subjective quality and consistency of the wind and wind gusts forecast from the participating WFOs has been quite good during the days leading up to the arrival of Hermine. Initial feedback from forecasters is that the process is improved over the standard methodology through the utilization of more science and much more collaboration. An example of the improved dialog between WFOs is shown in the AWIPS Collaboration tool chat from around 0330 UTC on 31 August in which forecasters are working together to ensure a consistent forecast more than 3 days in advance of the storm.

awips.collaboration.11pm.0830

Finally, I wanted to pass along a couple of images showing the end result of the forecast process. The image below shows the 33-hour forecast of wind (left) and wind gusts (right) from the NDFD valid at 09 UTC on 03 September. In these images, the wind and wind gusts are collaborated across 6 WFOs using the CSTAR methodology. These WFOs had to adjust the forecast for the high bias in the TCM product, inland decay of the TC, varying boundary-layer air masses, a pre-existing frontal zone, complex land-sea boundaries including the NC Sounds and the Chesapeake Bay while collaborating across 8 CWA boundaries. The end result appears to be a well collaborated forecast resulting from the hard work of the forecast staff on duty.

wind.wind.gust.5am.0903

A more formal evaluation of the process ad verification of the wind and wind gust forecast is planned after the storm. We’ll share those results on a future CIMMSE post.

Posted in CSTAR, TC Inland and Marine Winds, Uncategorized | Leave a comment

New Paper Comparing ASOS Near-Surface Winds and WSR-88D-Derived Wind Speeds in Landfalling Tropical Cyclones

tc.events

Map of ASOS and WSR-88D sites along with tropical cyclone tracks used in the study. 

A new article in Weather and Forecasting by Krupar et al. entitled “A Comparison of ASOS Near-Surface Winds and WSR-88D-Derived Wind Speed Profiles Measured in Landfalling Tropical Cyclones” may be of interest to some collaborators. The researchers made 22 comparisons during landfalling TC events in the Gulf of Mexico to compare low-level WSR-88D wind data with ASOS surface wind and wind gust observations within 10 km of the RDA. The goal was to develop an empirical relationship to relate the TC boundary layer wind to near surface winds. They found that radar based, site-specific linear regression equations using a 0–200-m layer average wind speed can be used to predict the ASOS 10-m standardized mean wind speed while a non-site-specific linear regression model using a VAD 0–500-m mean boundary layer wind can be used to predict ASOS 10-m nonstandardized gust wind speeds.

http://journals.ametsoc.org/doi/abs/10.1175/WAF-D-15-0162.1

Posted in TC Inland and Marine Winds, Uncategorized | Leave a comment

GOES-14 will be in Super Rapid Scan Operations Through August 25th

goes.srsor

GOES SRSOR visible satellite imagery from 1558 UTC 15 August 2016 in AWIPS

GOES-14 Super Rapid Scan Operations for GOES-R (SRSOR) began on 9 August and will continue for through 25 August 2016. Super Rapid Scan Operations (SRSO) will provide 1-minute imagery to support multiple research and GOES-R/S user readiness activities. The SRSO domain is usually selected a day or two in advance. The domain schedule along with selected imagery from prior days is available at: http://cimss.ssec.wisc.edu/goes/srsor2016/GOES-14_SRSOR.html#sched_and_movies  Additional background information including training and links to online imagery is available at: http://cimss.ssec.wisc.edu/goes/srsor2016/GOES-14_SRSOR.html

This will be a great opportunity to view the data over our region. NWS forecasters will be able to view some of this data in real-time in AWIPS-2. An example of GOES SRSOR imagery from AWIPS is shown in the image above.

Imagery including visible, infrared, and water vapor is available on the web at the links below…

Posted in Satellite | 2 Comments