No Storms in June...

[MWatkins]

Looks like we are easily going to make it through June with no named storms (or even a depression). I've looked through satellite imagery and the models and can find nothing but a fairly persistent pattern over the next 10 days or so.

So...interested to find out more about the 1995 season, particularly what happened in the lead up to the very active portion of the season, I stumbled across this musing from Gray in the 1995 June update.

Actually, there is a slight _negative_ association of early season storms (hurricanes) versus late season - August through November - r=-0.28 (-0.35). Thus, early season activity, be it very active or quite calm, has little or no bearing on the season as a whole.

Then, I was on to a Chris Landesa paper (who...IMHO does not get nearly enough praise or recognition for his work) that explains why a westerly QBO is an enhancement to hurricane activity when the notion of westerly winds across the Atlantic (as an enhancing factor), on the whole, is counterintuitive.

The stratospheric quasi-biennial oscillation (QBO) is an east-west oscillation of stratospheric winds that encircles the globe near the equator (Wallace 1973). The oscillation is asymmetric in time. The west phase at 30 mb typically lasts for 13 to 16 months, followed by a slow transition to the 12 to 15 month east phase, and then a relatively quick return to the west phase. Climatologically, easterly winds uniformly dominate the lower stratosphere over the MDR during the hurricane season. Thus the QBO west phase actually manifests itself as weak easterly winds at 30 and 50 mb (0 to -5 m s-1), while the east phase produces strong easterly winds (-20 to -30 m s-1) (Gray et al. 1992a). The west phase corresponds with increased Atlantic basin tropical cyclone activity and the east phase with reduced activity (Gray 1984a, Shapiro 1989).

Also, although this is 7/8 years old, Landesa floated the theory that the impact of the MJO may be minimal during the peak of the season:

In fact, Gray (1979) noted a clustering of tropical cyclogenesis on the time scales of a few weeks in both the Northern and Southern hemispheres. In the Indian and western Pacific, this clustering is often forced by the Madden-Julian Oscillation (MJO), with more than twice as many cyclones forming in the "wet" MJO phase than in the "dry" MJO phase (Liebmann et al. 1994). Shapiro and Goldenberg (1993) has shown, however, that the MJO is negligible in amplitude during the summer months over the Atlantic MDR. This suggests that the MJO may not be responsible for the intraseasonal variations in Atlantic tropical cyclones, though it does not discount the possibility that other intraseasonal variations in the atmospheric circulation may be tied to the "clustering" of Atlantic tropical cyclogenesis.

Just some stuff to read while things are so quiet. Here are the complete links to the references above...

http://cirrus.sprl.umich.edu/wxnet/gray.fcst

http://www.aoml.noaa.gov/hrd/Landsea/95Season/

MW

[Rainband]

Thanks MW

[Aquawind]

counterintuitive

..LOL.. Well said..

A couple of good points from those in depth articles..

Thanks for the info and chuckle..

[Anonymous]

This goes along with our June forecast. Looking good so far...

[Anonymous]

Then, I was on to a Chris Landesa paper (who...IMHO does not get nearly enough praise or recognition for his work) that explains why a westerly QBO is an enhancement to hurricane activity when the notion of westerly winds across the Atlantic (as an enhancing factor), on the whole, is counterintuitive.

The stratospheric quasi-biennial oscillation (QBO) is an east-west oscillation of stratospheric winds that encircles the globe near the equator (Wallace 1973). The oscillation is asymmetric in time. The west phase at 30 mb typically lasts for 13 to 16 months, followed by a slow transition to the 12 to 15 month east phase, and then a relatively quick return to the west phase. Climatologically, easterly winds uniformly dominate the lower stratosphere over the MDR during the hurricane season. Thus the QBO west phase actually manifests itself as weak easterly winds at 30 and 50 mb (0 to -5 m s-1), while the east phase produces strong easterly winds (-20 to -30 m s-1) (Gray et al. 1992a). The west phase corresponds with increased Atlantic basin tropical cyclone activity and the east phase with reduced activity (Gray 1984a, Shapiro 1989).

Landsea probably does deserve more credit. Sometimes I wonder how much Landsea helped Dr. Gray years ago. Gray's reports were a lot more detailed back then.

As for the QBO, I have another interesting link from Landsea.

The physical cause of these QBO-linked differences may be due to the contrasting stratospheric horizontal wind ventilation processes across the top of the hurricane, as illustrated in Fig. 2 and discussed by Gray (1988). During the east phase of the QBO, the absolute value of the stratospheric QBO winds at latitudes of 10°-15°N are strongly from the east. This condition causes net advection of hurricane structural elements that extend into the lower stratosphere away from the hurricane center. This relative advection is likely to act to restrain the stratospheric contribution to hurricane development and intensification. By contrast, during the west phase of the QBO, the absolute value of the zonal wind in the stratosphere (over hurricanes) at 10°- 15° N is weak. In this case, comparatively small horizontal wind ventilation may occur in the lower stratosphere (Fig. 2). This west-phase condition is a positive influence on the inner-core intensity of developing hurricanes. In this way the QBO west phase is a positive cyclone influence, and the east phase a negative influence. Additionally, it is possible that the QBO exerts other dynamical influences upon the largescale environment within which the hurricanes form. These involve hydrostatic height and temperature field differences associated with east and west phases of the QBO. Recent work (e.g., Gray et al. 1992a,b) shows support for these ideas; however, continued research into the QBO-tropical cyclone association is needed.

Figure 2: http://www.aoml.noaa.gov/hrd/Landsea/6- ... ure-2.html

Also, although this is 7/8 years old, Landesa floated the theory that the impact of the MJO may be minimal during the peak of the season:

The MJO is supposedly weaker during the summer months. But it does seem to have a noticeable influcence on Atlantic Basin activity. I have read season summaries that have mentioned the MJO as being the parameter that caused either a lull or spike in activity during the season. I believe 2000 was one of those years.

[MWatkins]

Landsea probably does deserve more credit. Sometimes I wonder how much Landsea helped Dr. Gray years ago. Gray's reports were a lot more detailed back then.

No question about that. He wrote the bible for internet hurricane enthusiasts...the hurricane FAQ on the NHC/TPC site (and elsewhere). There is stuff in there that EVERYONE following the tropics should read:

http://www.aoml.noaa.gov/hrd/tcfaq/tcfaqHED.html

MW