Newbie...Please Help me understand....

[Windtalker]

Since i'm new, I have some questions....The last STRONG La Nina was in 1988 and we only had 10 named storms that year...one being "Gilbert" a monster...how can everyone say that in a La Nina year to expect more storms..i'm alittle confused but what else is new...Thanks http://www.erh.noaa.gov/bgm/lanina.html ftp://ftp.nhc.noaa.gov/pub/storm_archiv ... at/atl1988

[mf_dolphin]

I think it's the absence of El Nino more than the presence of La Nina. Since we seem to be in the cycle of higher than normal tropical development, when you take away the inhibiting factor of an El Nino then people look for more potential activity.

[Guest]

ok, we had a La Nina that year, but what other factors occured. What direction was the QBO? The position of the Azores High? The SOI? Sea Surface Temps? But last but not least, what state was the Africa Sahel in, wet or dry?
I'm very busy these days, and if you look at those plus the NAO ect you will find that during 1988 taht some of these conditions where an inhibiting factor as MFDolphin suggested. We are currently foreseeing a neutral ENSO, meaning a La Nada, no La Nina or El Nino.

[Stormsfury]

Barometer Bob makes a great point on his post here ...

Let's also take into account 1995-1996 ...

ENSO conditions in 1995 were NEUTRAL ... ENSO conditions in 1996 was La Niña ..

1995's 19 storms, with the following year, 1996 having 13 storms ... however, 1996 was a LA NINA year, following a La Nada ... 2004 is NOT forecasted to be a La Nina year ... but let's breakdown 1995-1996 in regards to storms, the QBO indices, SST's, and the SOI indices ...

The QBO values were WESTERLY in 1995 in a neutral to slightly cold ENSO pattern and 1996 was a cold, weak ENSO (weak La Nina). However, in 1996 (indicated on the chart within the frame above, the QBO was STRONGLY EAST! ... Such as this year, yet, during BOTH 1996 and
2003, despite the Easterly QBO, other factors played in for quite an active CV season ...

SOI INDICIES ... By Month ...
|1995|-4.0|-2.7|3.5|-16.2|-9.0|-1.5|4.2|0.8|3.2|-1.3|1.3|-5.5|
|1996| 8.4| 1.1| 6.2| 7.8 | 1.3 |13.9|6.8|4.6|6.9|4.2|-0.1|7.2|

SST's Anomalies by month for 1995 ...
SST's Anomalies by month for 1996 ...

Also remember, since 1995, the ATL thermaline circulation has been stronger than normal ... not so in 1988 ...

Since 1995, we've seen 124 named storms, 69 hurricanes, and 31 majors... averaging 13 storms, 8 hurricanes, and 3 majors for 9 years. Furthermore, aside from 1997, 8 of the last 9 years have featured 10 or more ATL TC's, and the last six seasons have logged in 10 or more storms, which is also unprecedented.

[Guest]

But we're moving into a good westerly QBO now. Is that a reason for the cooler temps off the S. American west coast looking like a weak la nina? Hehe, I know the answer, just asking.

[USAwx1]

Hopefully this will help:

The ENSO cold phase describes the anomalous cooling of Sea Surface Temperatures over the equatorial Pacific, lasting between seven and fourteen months on average. Some events will be longer or shorter in duration than others. During these periods, anomalous low level easterly trade winds are observed across much across much of the Eastern Pacific, with enhanced westerly winds are noted near the tropopause in the upper levels of the atmosphere, this corresponds to the strengthening of the equatorial Walker circulation, particular to ENSO cold episodes.

ENSO cold conditions are characterized by a decrease in the depth of warm Sub-surface Ocean temperatures, and an increase in the slope of the equatorial thermocline, as well as a decrease in depth. Sea level height decreases across the eastern equatorial pacific which results in an increased slope in ocean surface heights over the basin. During strong ENSO cold episodes, the equatorial thermocline can become very close to the surface for extended periods of time. Decreased convection is seen across the eastern equatorial pacific, which corresponds with a westward placement of deep tropical moisture, convection and heating. The sub-tropical ridges retract as a result of the anomalous trophospheric heating in both the northern and southern hemisphere, where the resultant effect corresponds to a decrease in the north-south thermal gradient east of the dateline in the sub-tropical regions of both the northern and southern hemisphere, most specifically during the winter seasons. In these periods, the mean mid latitude jet undergoes a westward displacement, and an increased east-west contrast in both winds and temperatures is realized over both north and South America.

Large scale anomalous cyclonic circulations are observed in both hemispheres over the sub-tropical regions. This anomalous dipole of cyclonic circulations corresponds to enhanced easterly flow along the poleward flanks over the mid latitudes and westerlies across the eastern equatorial pacific. This pattern leads to the enhancement of the walker circulation, retraction of the sub-tropical ridge and mean wintertime jet west of the dateline.

Across the western tropical pacific, Indonesia and Eastern portions of the Indian Ocean, cold ENSO conditions feature anomalously above average rainfall and thunderstorm activity.

ENSO cold (La Nina) episodes are directly associated with decreased vertical shear across the Atlantic basin, which is favorable for Tropical Cyclone formation. Cold episodes also contribute to a more active Cape Verde season, more activity further south in the Atlantic basin, and a heightened probability for an above normal number of tropical cyclones overall.

Even still, La Nina conditions DON'T gurantee an active season, there are many other factors which must also be considered, for example the QBO, the PDO and ATC cycles...etc...

[USAwx1]

were also putting the caboose before the engine here WRT La Nina.

[Stormsfury]

(Before my PC crashed ... again)

Anyway, during ENSO NEUTRAL years ... take 1933, 1995, and 2003 for example ... we have seen those years produce quite a great number of TC's, but generally only half of those become hurricanes ...

1933 - 21/10/5 - less than 50% becoming hurricanes
1995 - 19/11/4 - slightly better than 50% becoming hurricanes
2003 - 16/07/3 - less than 50% becoming hurricanes

Now, the LA Niña years of 1988, 1996, 1998, and 1999 ... due to the general signature pattern, we generally see more in the way of blocking, and not quite so many TC's, and generally MORE TRUE Tropical Storms (ones developing below 20ºN) or developing in the deep Tropics. Secondly, we see a greater opportunity for these to develop into hurricanes due to the overall tendency of seeing much less shear than normal ...

1988 - 12/06/3 - ATL thermaline circulation weaker than normal. (50% becoming hurricanes)
1996 - 13/09/6 - Notice the ratio of tropical storms becoming hurricanes (and majors!)
1998 - 14/10/3 - Again, ratio of TC's becoming hurricanes
1999 - 12/08/5 - Again, 75% of TC's becoming hurricanes ...

Generally speaking, just because there is a La Niña year, doesn't guarantee that you'll see an outrageous amount of TC's that year, but the general idea is that the storms that do develop generally have a better than average chance of becoming hurricanes...statistically speaking.

SF

[*StOrmsPr*]

Since i'm new, I have some questions....The last STRONG La Nina was in 1988 and we only had 10 named storms that year...one being "Gilbert" a monster...how can everyone say that in a La Nina year to expect more storms..i'm alittle confused but what else is new...Thanks http://www.erh.noaa.gov/bgm/lanina.html ftp://ftp.nhc.noaa.gov/pub/storm_archiv ... at/atl1988

actually 12 storms, 5 canes = 3 intense canes (4-5) Also storm #6


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