UPDATE: Tropical Dolly forms in the Gulf

TROPICAL STORM DOLLY INTERMEDIATE ADVISORY NUMBER 3A
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052014
700 AM CDT TUE SEP 02 2014

…DOLLY HEADING TOWARD THE COAST OF MEXICO…
SUMMARY OF 700 AM CDT…1200 UTC…INFORMATION
———————————————-
LOCATION…23.0N 95.7W
ABOUT 145 MI…230 KM ESE OF LA PESCA MEXICO
MAXIMUM SUSTAINED WINDS…50 MPH…85 KM/H
PRESENT MOVEMENT…WNW OR 300 DEGREES AT 13 MPH…20 KM/H
MINIMUM CENTRAL PRESSURE…1005 MB…29.68 INCHES
WATCHES AND WARNINGS
——————–
CHANGES WITH THIS ADVISORY…

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT…

A TROPICAL STORM WARNING IS IN EFFECT FOR…
* TUXPAN TO BARRA EL MEZQUITAL MEXICO

A TROPICAL STORM WARNING MEANS THAT TROPICAL STORM CONDITIONS ARE
EXPECTED SOMEWHERE WITHIN THE WARNING AREA…IN THIS CASE WITHIN
THE NEXT 24 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA…PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.
DISCUSSION AND 48-HOUR OUTLOOK
——————————
AT 700 AM CDT…1200 UTC…THE CENTER OF TROPICAL STORM DOLLY WAS
LOCATED NEAR LATITUDE 23.0 NORTH…LONGITUDE 95.7 WEST. DOLLY IS
MOVING TOWARD THE WEST-NORTHWEST NEAR 13 MPH…20 KM/H…AND THIS
GENERAL MOTION SHOULD CONTINUE TODAY AND TONIGHT. ON THE FORECAST
TRACK… THE CENTER OF DOLLY WILL APPROACH THE COAST OF MEXICO
WITHIN THE WARNING AREA BY TONIGHT…AND MOVE INLAND BY WEDNESDAY
MORNING.

MAXIMUM SUSTAINED WINDS HAVE INCREASED TO NEAR 50 MPH…85 KM/H…
WITH HIGHER GUSTS. SOME ADDITIONAL STRENGTHENING IS POSSIBLE UNTIL
DOLLY MAKES LANDFALL.

TROPICAL-STORM-FORCE WINDS EXTEND OUTWARD UP TO 115 MILES…
185 KM…MAINLY NORTHEAST THROUGH SOUTHEAST OF THE CENTER.

THE MINIMUM CENTRAL PRESSURE REPORTED BY A RECONNAISSANCE AIRCRAFT
WAS 1005 MB…29.68 INCHES.
HAZARDS AFFECTING LAND
———————-
RAINFALL…DOLLY IS EXPECTED TO PRODUCE RAINFALL AMOUNTS OF
3 TO 6 INCHES WITH ISOLATED MAXIMUM AMOUNTS OF 10 INCHES ACROSS
SOUTHERN TAMAULIPAS…NORTHERN VERACRUZ…AND EASTERN SAN LUIS
POTOSI MEXICO THROUGH WEDNESDAY EVENING. THIS RAINFALL COULD CAUSE
LIFE-THREATENING FLASH FLOODS AND MUD SLIDES IN AREAS OF MOUNTAINOUS
TERRAIN.

WIND…TROPICAL STORM CONDITIONS ARE EXPECTED WITHIN THE WARNING
AREA BY TONIGHT.
NEXT ADVISORY
————-
NEXT COMPLETE ADVISORY…1000 AM CDT.

$$
FORECASTER PASCH

Invest 99L heads for Bay of Campeche

By Steve Gregory From Weather Underground

INVEST 99L NEAR YUCATAN – NO THREAT TO U.S.

INVEST 99L with a possible center of rotation near the northern Belize coast, is moving W/NW (300°) at 13Kts, slowing from its 20Kt forward motion just 24 hrs ago. The disturbance should slow further during the next 24-48 hrs as it crosses the Yucatan and emerges in the Bay of Campeche on Monday.

While wind shear remains marginally favorable for development at around 15Kts, with more than adequately warm SST’s near 85°F – upper level winds are not currently favorable for development since no anti-cyclonic ‘outflow’ exists. An anti-cyclone (High pressure) is needed at high levels (around 200mb – 40,000 ft) directly above a tropical cyclone in order to ‘vent’ the rapidly inrushing air found at the surface of a storm. Until some outflow develops, a significant cyclone will not be able to form.

By the time the disturbance reaches the Bay of Campeche tomorrow (Mon 1) , wind shear may fall off to as low as 5-10Kts, and upper level winds may become somewhat more favorable for the formation of a modest outflow pattern. In addition, due to the unique orientation of the topographical features found in the Bay – developing systems often have a propensity to ‘spin-up’ into tropical cyclones – though they rarely get beyond CAT 1 due to their proximity to rough terrain and the little time they usually have to intensify before going inland.

The Early cycle (12Z) model runs have a relatively wide spread in the projected tracks of the potential cyclone during the week ahead, but all show the system reaching Tropical Storm intensity. It’s worth mentioning that aside from the GFS – none of the global models, including the often overly zealous CMC – show any development of 99L – and even the GFS shows only modest development to possibly Depression strength. Regardless of development, the system is not expected to impact the US mainland.

SEVERAL TROPICAL WAVES ACROSS THE ATLANTIC

WITH A LARGE WAVE ALONG THE AFRICAN COAST

There are a couple other low latitude waves traveling across the central Atlantic, but none of them have shown any signs of development since yesterday. However, these systems are expected to reach the western CARIB by next weekend, where they may find upper level winds more conducive for development.

A VERY large tropical wave is along the West African coast, with some very deep convection (primarily still over land, though). This is the same system I referenced several days ago that was over eastern Africa where a strong AEJ (African Easterly Jet) was nosing into east/central Africa, and likely forced the development of the large wave we now see along the coast. In addition, this wave does NOT appear to be affected by the ‘warm and dusty’ Saharan Air Layer (SAL) which can inhibit cyclone formation.

But what is really unusual about this tropical wave is not its areal coverage – but the appearance of a well defined upper level anti-cyclone centered right above the strongest convection! I am hard pressed to recall seeing a similar situation. The question is whether this anti-cyclone (which didn’t exist yesterday morning) is actually ‘part of’ the disturbance’s overall structure, or if it’s simply an unrelated upper atmospheric feature that will not move in tandem with the lower level wave. We should have our answer by tomorrow as the tropical disturbance moves further out over the eastern Atlantic south/southwest of the Cape Verdes. All that said – without any low or mid-level rotation noted, development of this system, if any, will take some time. (None of the global models show any meaningful development of this particular system.)

IMAGES:

Fig 6: Sunday (31) mornings ‘Overview’ of the Tropical Atlantic includes a weak tropical wave along the north coast of south America (convection has weakened considerably over night) – along with 2 tropical waves in the central Atlantic which are westbound at 20-25 kts. Yesterday, this complex system had deeper convection, but I could only discern one primary wave. By this morning, however, further analysis has revealed this complex system consists of 2, separate, though inter-twined, wave structures. Or so it seems… But MOST interesting of all, is the very large tropical wave now emerging off the West African coast, and the fact that the SAL is NOT entrained in the overall structure of the disturbance – at least not yet!

Fig 7: The above color enhanced IR image over Africa reveals the deep convection associated with the very large tropical wave along the West African coast. This system is westbound at just over 20Kts.

Fig 8: The highest level winds (satellite derived) show a closed, anti-cyclone sitting atop the low/mid level disturbance – something I’ve rarely (if ever) seen. The lack of a low-mid level rotation, however, means any development of this system will be slow.

I’ll have an Interim update on 99L tomorrow, with a Full Tropical Update on Tuesday (2).

Steve

NOTE: I am issuing regularly Weather Updates 3-Days per week (Sundays, Tuesdays and Thursdays) – except when we have or expect active Tropical Cyclones in the Atlantic Basin – in which case Updates will be at least once daily. In addition, if a strong cyclone is expected to impact the US mainland – I will be posting my own detailed forecast charts. Go to: http://www.wunderground.com/blog/SteveGregory/

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