(ET) Streamline Configurations

1. H H (ET) Streamline Configurations H H Monsoon Trough C C Confluent Westerlies Tradewind Trough H

2. H H (ET) Streamline Configurations H H Monsoon Trough C C Confluent Westerlies Tradewind Trough H

3. Diurnal Effects • Temperature Range • Clouds • Rainfall

4. Diurnal Effects • Temperature Range • On small islands and coastlines 3-5°C with prevailing onshore flow. • On inland locations or coasts 5-10°C with prevailing land breeze. • In the interior in the dry season > 10°C.

5. Diurnal Effects • Clouds • Oceans • Maximum (0400-0700L), minimum (1400L-1900L) • Land • Daytime maximum, nocturnal minimum

6. Diurnal Effects • Rainfall • Nocturnal max over oceans, and small islands. • Shower maximum over land in afternoon. • Monsoon areas and areas in disturbances have night to early morning maximum.

7. Tertiary Circulations • Land and sea breezes • Sea-breeze characteristics. • Sets up a few hours after sunrise. • Moves inland until late afternoon to evening. • Strong breezes may extend 30 - 50 miles inland. • Land-breeze characteristics. • Generally shallower with weaker winds than sea breeze. • Normally does not penetrate as far offshore as sea breeze penetrates onshore. • Land breeze front often triggers convection, especially converging land breezes

8. Rainfall - Special Cases Prevailing flow onshore: Prevailing flow offshore Daytime max on inland slopes Afternoon max on coastline Day Sea Breeze Nighttime max on coastline Night Land Breeze

9. Sea Breeze

10. Sea Breeze

11. Land Breeze

12. Tertiary Circulations • Orographically-induced winds. • Valley breeze. • Slopes warm during day. • Upslope wind. • Clouds and convection over peaks during daytime. • Mountain breeze. • Slopes cool at night. • Downslope wind. • Clouds and convection in valleys at night.

13. Tertiary Circulations • Orographically-induced winds. • Mountain gap winds. • Funneling through passes when surface gradient across mountains is strong. • Example: Tehuantepecer winds off Mexico.

14. Tehuantepecers

15. Tehuantepecers

16. Tehuantepecers

17. Upper-Tropospheric Features • Tropical Upper-Tropospheric Trough (TUTT) • Forms in summer hemisphere over mid-oceans. • Subtropical ridge - part that moves poleward over land masses (North America, eastern Asia). • Subequatorial ridge - part that stays near equator over the ET.

18. Upper-Tropospheric Features • Tropical Upper-Tropospheric Trough (TUTT) - Continued - • Level: Most intense - 200 mb. • Orientation: ENE-WSW • Season: Late April - Mid November (most intense in August

19. Upper-Tropospheric Features • Tropical Upper-Tropospheric Trough (TUTT) - Continued - • Position: South of Surface Subtropical Ridge over trade winds (convergent weather associated with TUTT occurs in tradewinds) • Major Convergent Weather: Few degrees southeast of upper level center • Weather in axis or Cyclonic Cell Center: Few clouds, general sinking motion

20. Upper-Tropospheric Features • Tropical Upper-Tropospheric Trough (TUTT) - Continued - • Temperature: Cold trough (3-5 degrees colder than environment, Isold TCU and TSTMs in TUTT, and center of cells • Axis Windshift: Often an abrupt 180 degree turn at trough axis • Cirrus Tracers: Indicates > 50 kts either side of TUTT or embedded cell.

22. Overview • Upper-Tropospheric cyclones (cold lows). • Strongest 200 to 300 mb and weaken downward. • TUTT cells are most common examples. • Center • Usually clear due to subsidence, though deep cold cells can have some core convection. • Periphery • Upper-level divergence, mostly SE side. • Satellite Imagery • Ring of clouds about 140 nm from center. • Dark round area on water vapor image (best seen in water vapor!).

25. TUTT Cell

26. TUTT cell <------TUTT cell

27. TUTT Cell------>

28. TUTT Cell------>

29. TUTT Cell ---------->

30. TUTT Cell -----------> in Multispectral Imagery

31. NOGAPS 200 mb temperatures <-----Trough

32. Non-severe Weather Systems and Tertiary Circulations • Lines • Tropical Waves • Vortices • Land and Sea Breezes • Valley and Mountain Breezes

33. Non-severe Lines • Lines - synoptic scale convergence with length much greater than width. • Squall lines • Cold fronts • Shear lines • Surge Lines • Near Equatorial Convergence Zones

34. Shear Line

36. Non-Severe Tropical Waves • National Hurricane Center (NHC) definition - a trough or cyclonic curvature maximum in the trade-wind easterlies. • Sometimes called “Tropical Easterly Waves” in the Atlantic. • Originally, this term was based on older research on the tropics that was based on sparse surface and upper air data.

37. Non-Severe Tropical Waves • When NHC started using METSAT imagery in 1967, they saw new aspects of the so-called “wave” that didn’t fit the theoretical model. • Not as common as previously thought; many systems called waves were actually vortices • This model is falling out of favor with many in the tropical community.

38. The “Tropical Easterly Wave”

39. Non-Severe Tropical Waves • Characteristics • Many stem from upper-level cyclones (cold lows). • Characteristics of Atlantic (easterly) waves. • Form over Ethiopian Highlands June to October. • Move across baroclinic zone south of Sahara - often form squall lines. • Dampen under STR axis in eastern Atlantic and strengthen near Lesser Antilles.

40. Inverted “Vee” or Screaming Eagle - really a circulation

41. Screaming Eagle

42. Non-Severe Vortices • Fair weather vortices - (Equatorial anticyclone, heat low, and TUTT)… • Bad weather vortices - (Tropical cyclones, monsoon depression, west African cyclones, and mid Tropospheric cyclones).

43. Fair Weather Vortices • Equatorial anticyclones • Found where monsoon trough is more than 10° from equator • Surge from opposite hemisphere crosses equator and turns anticyclonically • Curved band of cloud seen at leading edge of anticyclone

44. Fair Weather Vortices • Heat lows/ heat troughs • Low-level air rises over hot land with subsidence aloft. • Lowest pressure coincides with highest temperature. • Examples • Sahara and SW Asia in summer (may be part of monsoon trough). • Southern South America, southern and eastern Africa all year.

45. Bad Weather Vortices • Mid-tropospheric cyclones. • Subtropical cyclones. • Cut-off portion of deep mid-latitude trough in the tropics in winter. • Example: "Kona" storms in Hawaii, cause SW winds and heavy rains. • Arabian Sea cyclones • Major rainmaker on west coast of India in SW monsoon. • Cloud pattern resembles a typhoon.

46. The Central American Monsoons • Regional Effects • Region normally dominated by NE trade winds. • Channeling causes 3 quasi stationary cyclones on Pacific side of Central America which anchor monsoon trough. • Northern Hemisphere easterlies to north and Southern Hemisphere westerlies to south maintain cyclones.

47. The Central American Monsoons • Panama Bay cyclone • Strongest anchoring cyclone of the three. • Reinforced by warm ocean currents. • Southwesterly flow channeled cyclonically by Andes year-round. • Persistent feature May through January.

48. The Central American Monsoons • Lake Nicaragua cyclone • Anchored between Nicaragua and Costa Rica. • Weaker than Panama bay cyclone, persists May - November. • Gulf of Tehuantepec (Guatemalan) cyclone. • Weakest of the three. • Maximum strength in October • Merges with NECZ to west, which is anchored over SST thermal maximum.

49. The Central American Monsoons • American Monsoons don't meet Ramage's Criteria because • Semi-annually reversing North-South pressure gradients do not form. • Instead, Central America has a "transitional" monsoon. • Oscillates north - south semiannually. • Location determined by strengths of NE trades and Southern Hemisphere southwesterlies.

50. The Central American Monsoons • Monsoon Surges • Often caused by low-latitude (10 - 20°N) tropical cyclones. • Acceleration of southwesterlies from south of monsoon trough. • NE flow aloft back into Southern Hemisphere.