Waterspout Forecasting Waterspout Forecasting A Gulf Coast Perspective and Modern A Gulf Coast Perspective and Modern

Day LookDay LookJeffrey M. MedlinJeffrey M. Medlin

NOAA - NWS Forecast OfficeNOAA - NWS Forecast OfficeMobile, ALMobile, AL

Jeffrey F. GarmonJeffrey F. GarmonNOAA – NWS Forecast OfficeNOAA – NWS Forecast Office

Cheyenne, WYCheyenne, WY

Tornado over the water…Tornado over the water…Possesses a parent mesocyclone: a much different animal.

Image Courtesy of WKRG TV, Mobile AL

Waterspouts…Waterspouts…

Wind speeds are more often under 100 KT. But…even these weaker circulations can cause damage and injury. [EF0 -> 65-85 mph, EF1-> 86-100 mph – most of what I’ve seen in 20+ years!]

On days of deeper instability forming over zones of stronger convergence…they can become quite strong with winds over 100 KT…posing a much greater hazard.

Several documented cases of waterspouts producing EF1/F-1 damage.

Tornadoes form under two regimes (Fujita, 1981)Tornadoes form under two regimes (Fujita, 1981)

• MesocycloneMesocyclone (diameter >4 km) “Supercell” (diameter >4 km) “Supercell”

• MisocycloneMisocyclone (diameter < 4 km) “Non-Supercell” (diameter < 4 km) “Non-Supercell”

MisocycloneMisocyclone circulations are the most probable mode of circulations are the most probable mode of formation for: formation for:

• ““landspouts” (Bluestein, 1985) and landspouts” (Bluestein, 1985) and

• ““waterspoutswaterspouts” ” (Wakimoto and Wilson, 1988). (Wakimoto and Wilson, 1988).

Mesocyclone versus MisocycloneMesocyclone versus Misocyclone

Not a gustnado either! . . .Not a gustnado either! . . .

Gustnado along a fast-moving Gustnado along a fast-moving squall line (M59 kt)squall line (M59 kt)Orange Beach, ALOrange Beach, AL

25 Apr 2015 – 2044 UTC25 Apr 2015 – 2044 UTC

Although some similarities!

Radar Observation of the Radar Observation of the CirculationCirculation

Waterspout circulation is much more Waterspout circulation is much more shallowshallow and is and is smallersmaller…therefore it will involve …therefore it will involve significant sampling issues due to beam significant sampling issues due to beam elevation and beam width with range.elevation and beam width with range.

Aspect Ratio (core dia. / beam width) prevents sampling of the phenomena much

beyond 40 km

In sample “A”…SW values would likely In sample “A”…SW values would likely be high…a tip off! be high…a tip off!

Climatology…Climatology…

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Jan Mar May Jul Sep Nov

Events

NWS Storm Data – NCDC database period 1995-2007Mobile, Baldwin, Escambia, Santa Rosa, and Okaloosa Counties

Landfalling waterspouts reported as tornadoes…Landfalling waterspouts reported as tornadoes…

A significant number of the warm season coastal “tornadoes” in the historical

database are in fact land-falling “fair weather” waterspouts.

Landfalling waterspouts reported as tornadoes…Landfalling waterspouts reported as tornadoes…

• A preliminary study conducted back in the 2003-2007 time frame revealed over half the time, when one waterspout was reported there were two or more (unpublished, Medlin and Caceres).

• There is a reason for this!There is a reason for this!

28.12 UTC

Textbook Example of Land and Sea-Breeze Circulation ReversalTextbook Example of Land and Sea-Breeze Circulation Reversal

Note how land Note how land breeze has shape of breeze has shape of the western Florida the western Florida Peninsula Coastline Peninsula Coastline

and it translates and it translates northwestward while northwestward while

becoming less becoming less defined with time as defined with time as heating occurs in its heating occurs in its

wake.wake.

Offshore –Offshore –directed directed

lower branch lower branch of land of land breeze breeze

circulation.circulation.

28 June 2012 – 12-16 UTC28 June 2012 – 12-16 UTC

28.14 UTC

28.15 UTC

First evidence of First evidence of new sea-breeze new sea-breeze

***Note*** wind reversal to ***Note*** wind reversal to “onshore” at a few locations “onshore” at a few locations along western FL coastlinealong western FL coastline

28.16 UTC

28.13 UTC 28.13 UTC PositionPosition

Waterspouts…Waterspouts… Formation aided by…Formation aided by…

• pre-existing vertical vorticity maxima pre-existing vertical vorticity maxima (e.g., existing (e.g., existing along a nocturnal land breeze boundary) which become along a nocturnal land breeze boundary) which become coincident with…coincident with…

• low-level updraftslow-level updrafts with TCu forming along the boundary. with TCu forming along the boundary.

Waterspouts have been observed to occur along Waterspouts have been observed to occur along thunderstorm thunderstorm outflow boundaries outflow boundaries and are formed by a and are formed by a similar process. similar process.

Another requirement for their occurrence is Another requirement for their occurrence is unstable unstable airmass airmass which enhances boundary layer updrafts, resulting which enhances boundary layer updrafts, resulting in vortex stretching. in vortex stretching.

Misocyclone formation…Misocyclone formation…

Wakimoto and Wilson, 1989Wakimoto and Wilson, 1989

In the case of most waterspouts…these boundaries can be an attendant land-breeze, seabreeze, or outflows from nearby convection.

Misocyclonic formation…Misocyclonic formation…

Wakimoto and Wilson, 1989Wakimoto and Wilson, 1989

See the link!See the link!

How most waterspouts form…How most waterspouts form…Brady and Szoke, 1989Brady and Szoke, 1989

Land-breeze or intersecting outflow boundaries establish zoneLand-breeze or intersecting outflow boundaries establish zone of weak low level horizontal circulationof weak low level horizontal circulation

““Convergence”Convergence”

How most waterspouts form…How most waterspouts form…Brady and Szoke, 1989Brady and Szoke, 1989

TCu forms along the convergent line…and updrafts with the TCu lift and stretch the horizontal circulation into the vertical.

“Vertical Advection of CirculationVertical Advection of Circulation”

How most waterspouts form…How most waterspouts form…Brady and Szoke, 1989Brady and Szoke, 1989

As the updraft increases, it stretches, tightens and strengthens the vortex. As the vortex velocity increases the condensation funnel forms.

““Stretching”Stretching”

Waterspout – 29 Aug 2003 – Downtown Mobile, AlabamaWaterspout – 29 Aug 2003 – Downtown Mobile, Alabama

Landspout – 14 June 2009 – Montgomery, AlabamaLandspout – 14 June 2009 – Montgomery, Alabama

Formed on a Progressive Derecho’s Gust Front!Formed on a Progressive Derecho’s Gust Front!

Photo courtesy Jennah MedlinPhoto courtesy Jennah Medlin

““Favored” Synoptic Environment for Favored” Synoptic Environment for Waterspouts… Waterspouts…

Deep layer ridging resulting in light winds surface to mid-Deep layer ridging resulting in light winds surface to mid-levelslevels

Moderate CAPE (especially packed low in sounding)Moderate CAPE (especially packed low in sounding)

Steep low level lapse ratesSteep low level lapse rates

Moist airmass (PW 1.7 - 2 inches)Moist airmass (PW 1.7 - 2 inches)

Presence of convergence zones (outflow boundaries, Presence of convergence zones (outflow boundaries, landbreeze)landbreeze)

Choy and Spratt (1994) Choy and Spratt (1994) identified some identified some conditions forecasters should look for…conditions forecasters should look for…

WINDWIND Boundary layer (0-1.0 kft): 8 knots or less Boundary layer (0-1.0 kft): 8 knots or less 975-700 mbs (1.5-10.0 kft): all levels 16 knots or less 975-700 mbs (1.5-10.0 kft): all levels 16 knots or less 699-600 mbs (10.5-14.0 kft): all levels 20 knots or less 699-600 mbs (10.5-14.0 kft): all levels 20 knots or less 599-500 mbs (14.5-18.0 kft): all levels 22 knots or less 599-500 mbs (14.5-18.0 kft): all levels 22 knots or less

MOISTUREMOISTURE Precipitable Water value: 1.7 inches or more.Precipitable Water value: 1.7 inches or more.

Essential Tools Include…Essential Tools Include… RAOBs RAOBs

88D88D• VWPVWP• ZZ• SWSW• SRM (limited)SRM (limited)

Higher resolution satellite imagery Higher resolution satellite imagery • Early morning low cloud channel Early morning low cloud channel • Daytime visible Daytime visible

Surface observations Surface observations • Tap into local mesonet and offshore dataTap into local mesonet and offshore data

Coastal spotter networkCoastal spotter network• U.S. Coast Guard (reports from VHF 16).U.S. Coast Guard (reports from VHF 16).• Life guard networks at area beaches. Life guard networks at area beaches.

Local meso-scale analysis and forecast tools Local meso-scale analysis and forecast tools • Well initialized local WRF runsWell initialized local WRF runs• AWIPS LAPS data with quality controlled observational inputs. AWIPS LAPS data with quality controlled observational inputs.

Thermal, Moisture and Wind Thermal, Moisture and Wind Profiles…Profiles…

Shallow, steeper low level lapse rate just above

the surface.

Light easterly tropical flow is conducive to organizing landbreeze

convergent lines offshore OROR no flow at all!

Convergent TCU Zones…Convergent TCU Zones…

Visible imagery shows location of convergent lines where TCu is growing.

88D reflectivity shows where the showers are organizing along the convergence

lines.

NEXRAD shows where showers NEXRAD shows where showers are forming along the TCu line…are forming along the TCu line…

Strengthening updrafts along the remnant land breeze convergent zone

Some studies have shown that intersecting

boundaries will focus misocyclone formation

(Wakimoto and Wilson, 1989).

SRM data won’t likely show the SRM data won’t likely show the circulation…circulation…

…the TCu and showers are forming on the boundary 40-55 nm from the radar site…and the circulation is probably not being sampled due to range and aspect ratio considerations.

However, if the radar site is within 40 nm of the report or suspect area…Spectrum Width (SW) data may help!

Waterspout – 12 Oct 2009 – Mobile BayWaterspout – 12 Oct 2009 – Mobile Bay

Waterspout – 12 Oct 2009 – Mobile BayWaterspout – 12 Oct 2009 – Mobile Bay1455 UTC1455 UTC

Waterspout – 12 Oct 2009 – Mobile BayWaterspout – 12 Oct 2009 – Mobile Bay

1455 UTC1455 UTC

Waterspout – 12 Oct 2009 – Mobile BayWaterspout – 12 Oct 2009 – Mobile Bay

1459 UTC1459 UTC

Waterspout – 12 Oct 2009 – Mobile BayWaterspout – 12 Oct 2009 – Mobile Bay

1503 UTC1503 UTC

Waterspout – 12 Oct 2009 – Mobile BayWaterspout – 12 Oct 2009 – Mobile Bay

1508 UTC1508 UTC

Radar Observation of the Radar Observation of the MisocycloneMisocyclone

From Wakimoto and Wilson, 1988:From Wakimoto and Wilson, 1988:

• Radar vortex can precede visual vortex by 14 mins… Radar vortex can precede visual vortex by 14 mins… but…but…

• Vortices are shallow and small forming Vortices are shallow and small forming below 2 km… below 2 km… (dia <2 km)(dia <2 km)

• Average maximum horizontal shear=.062 s-1Average maximum horizontal shear=.062 s-1

• Parent cloud is often Cu that evolve into CB at a later Parent cloud is often Cu that evolve into CB at a later stagestage

88D Strategy…88D Strategy… High resolution radar reflectivity data High resolution radar reflectivity data can show can show

boundaries better…a significant improvement. boundaries better…a significant improvement. • 0.5 degree/0.25 km resolution versus 1 degree/1 km legacy.0.5 degree/0.25 km resolution versus 1 degree/1 km legacy.

SamplingSampling - Beam elevation and aspect ratio - Beam elevation and aspect ratio considerations will limit detection with SRM data. considerations will limit detection with SRM data. Weak circulations close to the radar may be Weak circulations close to the radar may be evident…but not likely sampled adequately. evident…but not likely sampled adequately.

Spectrum Width (SW) Spectrum Width (SW) can be useful can be useful in detection of in detection of suspect areas…if the suspect area is close enough to suspect areas…if the suspect area is close enough to the radar. the radar.

Forecasters now have some powerful tools to Forecasters now have some powerful tools to better forecast and detect the coastal waterspout better forecast and detect the coastal waterspout

environment…environment…

AWIPS 5 km LAPS analysis of wind, convergence, instability, etc.

Local higher 5 km resolution WRF model runs that give guidance on convergence

zones, instability, and wind profiles.

Identifying Waterspout DaysIdentifying Waterspout Days

or... HWO

0-24 h0-24 h1-3 h1-3 h

On Polygon Warnings for WaterspoutsOn Polygon Warnings for Waterspouts

Tornado Warning for Land-falling waterspout…

More on TOR vs. SMWsMore on TOR vs. SMWs

•Golden has documented up to 85 m/s (or ~190 kt) in large FL Keys waterspouts!

•NWSI SMW and SVR Chapters for a TOR does not elaborate on exactly what action to take (very nebulous).

•For WFO MOB, we typically issue a SMW for a land-falling waterspout (i.e., a non-supercell tornado process), unless we have some evidence that it is very large and\or life-threatening because most of the time they dissipate immediately and winds are much less than 60 mph.

•FAR problem (especially public perception), and it usually dissipates right on the beach. By the time a warning would be issued, it would be gone!

We’ve progressed in the last 20 We’ve progressed in the last 20 years with…years with…

Better understanding of the environment they form in…Better understanding of the environment they form in…

Higher resolution radar data allowing for better identification of Higher resolution radar data allowing for better identification of boundaries…boundaries…

Higher resolution satellite data…Higher resolution satellite data…

Better educated spotters along the coast…Better educated spotters along the coast…

Last but not least…our higher resolution mesoscale models (such Last but not least…our higher resolution mesoscale models (such as the local WRF and now HRRR) and other analysis tools (e.g., as the local WRF and now HRRR) and other analysis tools (e.g., LAPS) have brought a plethora of new tools to the forecast desk.LAPS) have brought a plethora of new tools to the forecast desk.

ReferencesReferences Golden, J.H. (1971): “Tornadoes and Waterspouts over South Golden, J.H. (1971): “Tornadoes and Waterspouts over South

Florida”, AMS Florida”, AMS Monthly Weather ReviewMonthly Weather Review 99: 146-154 99: 146-154

Golden, J.H. (1977): “An Assessment of Waterspout Frequencies Golden, J.H. (1977): “An Assessment of Waterspout Frequencies Along the U.S. East and Gulf Coasts”, AMS Along the U.S. East and Gulf Coasts”, AMS Journal of Applied Journal of Applied MeteorologyMeteorology 16: 231-236 16: 231-236

Wakimoto, R.M., Wilson, J.W. (1989): “Non-Supercell Tornadoes” Wakimoto, R.M., Wilson, J.W. (1989): “Non-Supercell Tornadoes” AMS AMS Monthly Weather ReviewMonthly Weather Review 117: 1113-1140 117: 1113-1140

Brady, R.H., Szoke, E.J. (1989): “A Case Study of Non-Mesocyclone Brady, R.H., Szoke, E.J. (1989): “A Case Study of Non-Mesocyclone Tornado Development in Northeast Colorado: Similarities to Tornado Development in Northeast Colorado: Similarities to Waterspout Formation” AMS Waterspout Formation” AMS Monthly Weather ReviewMonthly Weather Review 117: 843- 117: 843-856856

Choy, LT(jg) B.K., Spratt, S.M. (1994): “A WSR-88D Approach to Choy, LT(jg) B.K., Spratt, S.M. (1994): “A WSR-88D Approach to Waterspout Forecasting” Waterspout Forecasting” NOAA Technical MemorandumNOAA Technical Memorandum NWS SR- NWS SR-156 156

ReferencesReferences Burgess, D.W., Donaldson, R.J. Jr., Desrochers, P.R. (1993): Burgess, D.W., Donaldson, R.J. Jr., Desrochers, P.R. (1993):

“Tornado Detection and Warning by Radar” “Tornado Detection and Warning by Radar” Geophysical Geophysical MonographMonograph 79: 203-221 79: 203-221

Caruso, J.M., and Davies, J.M., (2005): “Tornadoes in Non-Caruso, J.M., and Davies, J.M., (2005): “Tornadoes in Non-mesocyclone Environments with Pre-existing Vertical Vorticity mesocyclone Environments with Pre-existing Vertical Vorticity along Convergence Boundaries”: NWA along Convergence Boundaries”: NWA Journal of Operational Journal of Operational Meteorology.Meteorology.

Fujita, T., (1981): “Tornadoes and downbursts in the context of Fujita, T., (1981): “Tornadoes and downbursts in the context of generalized planetary scales.” AMS generalized planetary scales.” AMS Journal of Atmospheric Science Journal of Atmospheric Science 38: 1511-1534.38: 1511-1534.

Central Gulf Coast Waterspouts…Central Gulf Coast Waterspouts…