Weather456's Tropical Weather Blog

Tropical MetEd: Upper Level Low Transition to Tropical Cyclone

By: Weather456, 2:45 AM GMT on September 29, 2007

Upper Level Lows

In comparison to its environment, this low is most intense and coldest in the upper troposphere. Thus it is weaker at lower levels and can be hard to find below 500 mb. Apart from a few cumulonimbus that may form near the center, it is generally subsident and cloud free, except for rising motion and cloud on its eastern periphery. In summer over the tropical Atlantic and Pacific Oceans, and the South Indian Ocean, a line of cold lows may comprise the TROPICAL UPPER TROPOSPHERIC TROUGH (TUTT).

Sometimes these upper level lows transform themselves into warm-core system given in the three stages below.

Stage 1

In the upper cell, 500 to 1000 NM (1000 to 2000 km) across, winds reach 40 knots or more in all quadrants. Flow diverges east and southeast of the center, generally accelerating downstream toward the strong southwesterlies of the TUTT to the east. Beneath it, the divergence induces a trough that extends up to 700 mb. This is where organized convection is first observed. Locating the clouds with respect to the low-level trough is difficult because, at this stage, the trough is weak. Whether the extensive convection, initiated from aloft, develops prior to the surface trough cannot be determined from available observations.

Stage 2

Organized convection beneath the upper divergence east of the upper cell significantly expands. This in turn alters the upper-level flow as the resulting heating due to condensation builds a sharp ridge east-northeast of the cell, forces the cell northward and splits the TUTT. At the same time, the cold low shrinks and no longer penetrates down to the 500 mb level. In low levels, the wave develops into a weak depression with a closed vortex below 500 mb. The main convective cloud lies east of the low-level vortex. Other clouds may be distributed around the circulation.

Stage 3

Upper-tropospheric flow becomes more complex as increased convection intensifies the ridge or even builds an anticyclone whose outflow interacts with and further distorts the TUTT. In the western end of the northern branch a small cyclone often forms, with its own cloud system. The model only depicts it for stage 3, but it may occur in stage 2. In the lower layers, the depression becomes a tropical storm extending up through 500 mb and capped by an anticyclone. The upper outflow is not impeded to the east where it merges with the larger scale westerlies south of the TUTT, and so the cirrus shield is skewed toward the east. North of about 15N, storms that are triggered by cold lows in the upper trough cannot tap an upper-level outflow channel to the south into large-scale easterlies. Perhaps this is why these storms seldom intensify into strong typhoons.

Tropics Summary: Ingrid/93L/Hurricane Ivo/N ATL Low Pressure

By: Weather456, 10:01 PM GMT on September 20, 2007

An upper level low continues to interact with a surface low pressure area near 27N/83W and an associated surface trough extending south-southwestward across the Western tip of Cuba into the Northwest Caribbean. Clear cyclonic turning is evident on satellite imagery with light to moderate showers across the area from West Florida to 87W south of 30N. Though the system remains disorganize and so development is not expected any time soon.

Enviromental conditions are favorable for further development and AMSU data of 200 mb and 100 mb temperature along with cyclone phase diagrams from FSU suggest the cyclone is becoming tropical. Also surface observations show winds generally centered near the center.


Showers have diminish with the remnant circulation of Ingrid and regeneration is unlikely. Still the area may need to be watch incase something pops up.

Hurricane Ivo

On September 18, Tropical Depression Twelve-E formed about 670 miles south-southeast of the southern tip of Baja California. Later the same day it was upgraded to Tropical Storm Ivo, and it reached hurricane strength the next day.

Current storm information
As of 2 p.m. PDT (2100 UTC) September 20, the center of Hurricane Ivo is estimated to be located within 25 nm of 17.8N 113.1W. Hurricane Ivo has maximum sustained winds of 70 kt (80 mph, 130 km/h), with higher gusts. It has a minimum central pressure of 981 mbar (28.97 inches), and is moving NNW at 6 kt (7 mph, 11 km/h).

Hurricane Ivo is expected to move towards the coast of Baja Peninsula bringing atleast tropical storm-forced winds to the area and 1-2 inches of rain.

Non Tropical Low

A non tropical low near 31N/49W in association with a surface trough exnteding to the SW near 17N/55W has the potential to develop into a subtropical or tropical cyclone during the next couple of days. I will have more on this interesting feature as more data becomes avaible.

93L Invest

AMSU-A Channel 7 (54.94GHz) 200 mb

NOAA visible Image of Hurricane Ivo

Tropical Storm Force Wind Speed Probabilities - 120 Hours

Non Tropical Low


By: Weather456, 9:07 PM GMT on September 19, 2007

Never thought a funny comic would get me banned from Dr Master blog but it did. If the comic was inappropriate to anyone, I'm sorry and didnt mean any harm, just thoought it would be funny to help ease some ppl from the diliema of 93L.


Ingrid Regenerating?

An upper trough/low just north of Puerto Rico is interacting with a 1012 millibar surface low near 22N/63W (the remnants of Ingrid) resulting in scattered showers and thunderstorms just to the north of the Northern Leeward Islands. The last quikscat from this morning showed the center is still evident. In addition to that, convergence, vorticity and pressure tendencies are in agreement that the circulation maybe becoming better organize. Convection is not too impressive this evening but enviromental conditions are favorable for a tropical depression to form. It is uncertain whether it will be rename but the circulation was evident for most of the time so that seems unlikely.

A new quikscat pass is schedule for later tonight and it should shed some light on the status of Ingrid.

I will have an update on 93L later tonight or tommorrow.


The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Weather456's Tropical Weather Blog

About Weather456

With a Bachelors Degree in Environmental Sciences (2009), began tracking tropical storms in 2002 and is now a private forecaster.