Enhanced Northeasterly Winds in the Western Gulf of Maine

1. Enhanced Northeasterly Winds in the Western Gulf of Maine Daniel Michaud Samuel Miller Plymouth State University Dan St. Jean NOAA/NWS Gray ME NROW IX – November 7, 2007

2. COMET Partners Projects • 2 COMET Partners grants have supported this research in 2006-07 and 2007-08 • 6 PSU students, 1 PSU professor and 2 NWS forecasters have collaborated on this research

3. Outline • Introduction and Background • Methodology • Results • Predictability • Conceptual Models • Future Work • Summary • Acknowledgements

4. Area of Study • Map courtesy of GoMOOS

5. The Northeasterly Wind Phenomenon • A near-surface, near-shore, mesoscale band of enhanced northeasterly wind in the western Gulf of Maine (GoM) • This flow is not predicted well by NWP or forecasters…and is typically under-forecast

6. Why Study This Phenomenon? • Some possible ramifications of the under-prediction of northeast winds: • Increased wave heights, both due to higher winds and longer duration • Increased storm surge during larger events • All of the above can put property and life at risk, especially when the conditions deviate significantly from the forecast

7. Example – 23 May 2005 • A Small Craft Advisory and then a Gale Warning were raised for the western GoM coastal waters • A tight gradient northwest of a deep cyclone in the GoM • Winds increased and far exceeded all human and numerical predictions • $1M USD in damage to marinas and beaches • Peak MOS winds were ~20 kts, peak forecaster winds were 20-25 kts for the 24 hrs prior to event onset • Winds peaked at 46G51 kts at Matinicus Rock (MISM1), 43G49 kts at Isles of Shoals (IOSN3) • Over 12 hours of winds greater than 30 kts in GoM

8. Background • Apffel (2006) showed in a GYX study: • NWP, and consequently human forecasters, do not capture these northeast wind events well • Guidance consistently under-predicts northeast winds in the western GoM • In northeast flow…GFS MOS has a bias of -5kt and mean error of 4kt • A cause for concern and study

9. Example of GFS MOS Bias • This is a graph of GFS MOS error and bias over a 1.5 year period at Isle of Shoals (IOSN3) • The largest model error was seen in NE flow • A strong negative bias in flow speed was also observed in NE flow Apffel, 2006 ETA MOS has the same negative bias in NE flow…so what do forecasters use?

10. Background • Why doesn’t MOS – and other guidance – not handle NE winds well in the GoM? • Possibly due to sub-grid scale phenomena (coastal front, terrain effects) not being handled well by NWP • Shallow air masses (typically arctic/polar in nature) cause mesoscale northeast winds that are not shown well by models • Small, elusive coastal fronts/baroclinic zones can significantly increase wind speed and affect flow direction over the coastal waters • Biased model output creates a systematic error in which the forecasters under-forecast both wind speed and duration in NE flow over the GoM

11. Background • Previous studies by Apffel (2005), Moker (2006) and Michaud (2006, 2007) have shown that both synoptic and mesoscale pattern recognition can prove useful in detecting these events

12. Background • Using these prior studies it was determined: • The synoptic and mesoscale conditions are important • The wind events are likely caused by a combination of synoptic and mesoscale forcing • An expected outcome includes an improved technique to forecast these wind events • Including improving forecaster focus/situation awareness leading up to a possible event

13. Methodology • 5-year dataset of wind observations from both onshore and offshore stations was used • Criteria : • Sustained wind in excess of 6 ms-1 at all three offshore stations (IOSN3, 44007, MISM1) concurrently • Wind direction between 15 and 75 degrees true • The above conditions must be met for 3 consecutive hours to begin an event • A break of one station for one hour was allowed to continue as a single event

14. Methodology • Based on those criteria there were more than 100 wind events totaling over 500 hours • Synoptic classification scheme was created which could explain the pre-onset evolution of these events • Vertical wind structure, surface wind and temperature, surface sea-level pressure pattern analyzed • This was done to find the cause of forcing for wind events, e.g. coastal front or baroclinic zone, shallow frontal surface, shallow high pressure/cold air mass, synoptic flow • Used various datasets ranging from NARR to archived upper air soundings to surface analyses/observations • NWS marine verification program showed model biases in NE flow

15. How have the events been classified? • Moker (2006) quadrant system • Each case was placed into a synoptic classification based on its orientation relative to these quadrants

16. Example: Scenario 1 • This is the case that is most obvious for a northeast flow over the western GoM • However, this scenario only accounts for 26% of all cases • - Flow is near-geostrophic in the GoM

17. LEGEND: : 925 hPa wind maximum (m/s) 7 Times are in hours before onset Last wind maxima is at event onset, previous maxima plotted every 12 hrs

18. Synoptic Classification Results • Synoptic classification system works for rough pattern recognition within 24-48 hours • Still doesn’t explain the key mesoscale features responsible for the enhanced NE winds • Synoptic-scale pressure gradients are too weak to explain what’s happening on the mesoscale

19. Example of a synoptically-driven event Winds at 925 and 1000 hPa are both NE Deepening synoptic low to the southeast Northeast winds @ 10-20 kt have developed from the Maritimes through all of New England and coastal waters No presence of a coastal front or baroclinic zone

20. Example of a shallow cold air/surface high pressure-driven event Westerly 850 hPa flow at 15 kt Flow turns to a light E flow at 5 kt Temps near 45° offshore 30° at coastal locations 0° on Canadian border H Surface winds NE 15-20 kt after frontal passage 1000 hPa flow out of NE at 10 kt Strong baroclinic zone along coastal plain

21. Coastal Front Case Study:26 December 2004

22. 26 December 2004 Event T-24h T-12h T-0h

23. 26 December 2004 Event T-24h T-12h T-0h Northeast winds have begun blowing, as a low pressure develops near Tampa FL A trough ahead of the storm focuses higher winds and surface convergence Very strong northeast winds hit the GoM, gusts to 56 kts at several buoys, sustained to 45 kts Forecasters expect winds to reach gale force (30-35 kt), matching guidance A storm warning is raised only after the near-coast winds increase well beyond guidance and forecast Forecasters expect 30-40 kt winds, raise gale warning

24. 26 December 2004 Event T-36hr: SUN...E WINDS 10 TO 15 KT...BECOMING NE 15 TO 20 KT IN THE AFTERNOON. SEAS 4 TO 6 FT. SUN NIGHT...NE WINDS 15 TO 20 KT WITH GUSTS TO 25 KT. SEAS 5 TO 8 FT. MON...NE WINDS 20 TO 25 KT...DECREASING TO 15 TO 20 KT IN THE AFTERNOON. SEAS 3 TO 6 FT. T-12hr: Small Craft Advisory SUN...NE WINDS 20 TO 25 KT...INCREASING TO 25 TO 30 KT. SEAS 5 TO 8 FT. SUN NIGHT...N WINDS 25 TO 30 KT...INCREASING TO 30 TO 35 KT. SEAS 7 TO 10 FT. MON...N WINDS 30 TO 35 KT WITH GUSTS TO 40 KT. SEAS 7 TO 10 FT. T-6hr: Gale Warning TODAY...NE WINDS 25 TO 35 KT. SEAS 6 TO 10 FT. TONIGHT...NE WINDS 30 TO 40 KT...BECOMING N AFTER MIDNIGHT. SEAS BUILDING TO 8 TO 12 FT. MON...N WINDS 25 TO 30 KT. SEAS 7 TO 10 FT. T+6hr: Gale Warning TONIGHT...NE WINDS 30 TO 40 KT...WITH GUSTS TO 45 KT...BECOMING N AFTER MIDNIGHT. SEAS 8 TO 13 FT. MON...N WINDS 30 TO 40 KT. SEAS 9 TO 14 FT.

25. 26 December 2004 Event T+12hr: Storm Warning TONIGHT...NE WINDS 40 TO 50 KT WITH GUSTS TO 60 KT. WINDS BACKING TO THE N BY MORNING. SEAS 12 TO 18 FT. MON...N WINDS DIMINISHING TO 30 TO 40 KT EARLY...THEN BECOMING NW 25 TO 30 KT IN THE AFTERNOON. SEAS 12 TO 18 FT. T+16hr: Storm Warning TODAY...N TO NE WINDS 40 TO 50 KT WITH GUSTS TO 60 KT... BECOMING NW 25 TO 35 KT LATE. SEAS 15 TO 22 FT.

26. 24 hours prior to onset 1000 hPa winds (m s-1) Surface Analysis

27. 12 hours prior to onset Surface trough analyzed 1000 hPa winds (m s-1) Surface Analysis

28. Event onset Coastal Front Rapid wind speed increase Surface Analysis 1000 hPa winds (m s-1) Within the next 6-12 hrs surface winds reached borderline storm force criteria At this time surface winds had reached 30-40 kts sustained

29. Event Onset 6 9 850 hPa 925 hPa Surface winds are sustained 15-20+ ms-1…faster winds are not transported downward Mean wind speed over western GoM, in m s-1 9 1000 hPa

30. 12Z Dec 26 2004 – KGYX Sounding Inversion Winds at KGYX are weaker than over coastal waters Wind Shear

31. Post-frontal Case Study:15 January 2001

32. 15 January 2001 Event T-24h T-12h T-0h

33. 15 January 2001 Event T-24h T-12h T-0h Alberta clipper is racing east, w/ arctic cold front across southern Quebec Arctic front poised across the northern mountains, weak W wind Northeast winds begin at all locations at this time, 15-25 G 35 kt offshore Small craft advisory raised for increasing seas and higher winds Forecast now calls for E-NE winds 15-25 kt overlapping two periods Forecast for a period (12 hrs) of E to NE wind, 15-25 kt

34. 15 January 2001 Event T-24hr: MONDAY...E TO NE WIND 15 TO 25 KTS. AVG SEAS 2 TO 4 FT. T-12hr: MONDAY...E TO NE WIND 10 TO 20 KTS. AVG SEAS 2 TO 4 FT. MONDAY NIGHT...E WIND 15 TO 25 KTS. AVG SEAS 3 TO 6 FT. T-0hr: SMALL CRAFT ADVISORY TODAY...NE WIND 15 TO 25 KTS WITH A FEW HIGHER GUSTS... VEERING TO THE E. AVG SEAS 3 TO 6 FT. TONIGHT...E WIND 15 TO 25 KTS WITH A FEW HIGHER GUSTS. T+6hr: SMALL CRAFT ADVISORY TONIGHT...E TO NE WIND 15 TO 25 KTS WITH A FEW HIGHER GUSTS. AVG SEAS 3 TO 6 FT. T+12hr: SMALL CRAFT ADVISORY OVERNIGHT...MERRIMACK RIVER MA TO BOOTHBAY HARBOR ME...N WINDS 20 TO 25 KTS...BECOMING NW. AVG SEAS 4 TO 6 FT. BOOTHBAY HARBOR ME TO STONINGTON ME...E TO NE WINDS 20 TO 25 KTS. AVG SEAS 4 TO 6 FT. Long Lead Time of 30 hrs for this event

35. Before and After Cold Frontal Passage

36. Case Study Results • Forcing for NE wind events is near-surface • Winds aloft in the majority of events were weak • Rules out downward momentum transfer arguments • Mesoscale gradients and boundaries are likely the main contributors

37. How Predictable? • Most events predictable on synoptic scale • Guidance typically signals NE flow 24-36 hrs in advance • Guidance wind speed generally too low and attempts to ‘catch up’ as event unfolds • Duration of NE winds often outlasts what guidance is showing…many cases involved NE flow as long as 12-24 hours after MOS shows a shift to E, SE, N

38. More on Predictability • Remember MOS has strong negative bias in NE flow • Forecasters can hedge on the higher side…especially when a subtle feature (such as a coastal front, shallow frontal sfc) are in play • When NWP is indicating stronger NE flow…pay attention! • Does the model solution make sense – is the model onto something, like a tightening surface pressure gradient? • Subtle features do matter: • If a coastal zone of convergence and/or a strong thermal contrast exist, this can amplify the pressure gradient & wind speed and turn the flow direction along-shore (i.e., NE)

39. Conceptual Model: A Plan View H H L Low pressure develops, moves S/E of the GoM High pressure moves S/E out of Canada Cold front dives S/E across the region OR stnry/warm front S/E of coastal waters High pressure builds in from Canada

40. Conceptual Model: A Cross-section View • In this case we have a coastal front/baroclinic zone trapped at the shore • The near-surface NE flow develops seaward of the front & behind cold/warm/stnry front well offshore • The front becomes a focus of convergence, light precip • Coastal land-based stations report a light N-NW wind in most of these situations Directional shear with height across inversion sfc NW, W, SW FLOW ABOVE INVERSION Inversion SHALLOW, COLDER/ ARCTIC AIR MASS MODIFIED, WARMER AIR MASS Light N/NW flow NE FLOW Coastal Front KRKD KPWM KPSM MISM1 44007 IOSN3

41. Conceptual Model: A Cross-section View • In this case we have two situations to consider, either: • A coastal front is along or inland of the shore, or • No coastal front exists • In the first situation there is a trapped band of NE flow below inversion/front • The second situation is dominated by a general NE flow both offshore and onshore Directional shear with height across inversion sfc N, NW, W, SW FLOW ALOFT/INLAND Inversion COOLER, MODIFIED AIR NE FLOW Coastal Front (?) WARMER AIR KRKD KPWM KPSM MISM1 44007 IOSN3

42. Current/Future Work • Current COMET grant focusing on the mesoscale structure of NE wind events • Deriving equations to calculate gradients and expected flow strength based on gradients • These will be calculated based on model output and real-time observations • NWS Gray developing GoM NE wind guidance/reference for improving situation awareness and predictability

43. Summary • Models are biased in NE flow in the western Gulf of Maine • Forecasters consequently have not anticipated higher NE wind speeds • Both synoptic and mesoscale conditions important in forcing NE wind • Situation awareness and familiarity are key • Forecasters need to anticipate the mesoscale features that can shift winds to NE and enhance their speeds

44. Acknowledgements • Daniel Michaud • 2007 NOAA Hollings Scholar at NWS Gray • Dr. Sam T.K. Miller • Research Advisor, Professor of Meteorology, Plymouth State • A host of graduate/undergraduate PSU students who laid the groundwork for this research • COMET Partners Program • NOAA Hollings Scholarship Program