Tropical weather analysis - September 3, 2014

By: KoritheMan , 5:35 AM GMT on September 03, 2014

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Dolly

Tropical Storm Dolly has made landfall. As of the 0300Z NHC advisory, the following information was posted on the cyclone:

Wind: 45 mph, with higher gusts
Location: 21.9°N 97.7°W
Movement: W at 9 mph
Pressure: 1002 mb

Satellite and radar data suggest that the center of Dolly made landfall along the eastern coast of Mexico between Tampico and Tuxpan around 0400 UTC. At the time of landfall, the heaviest precipitation and the strongest winds were not found near the center, but instead limited to convective bands south and east of the center. This is likely due to continued northerly shear on the backside of a mid- to upper-level ridge over Mexico extending westward from a rather expansive and deep subtropical ridge from the Bahamas westward to the Texas coast, and also due to that same ridge amplifying the horizontal pressure gradient to the east of the storm.



Figure 1. Latest infrared satellite image of Tropical Storm Dolly. Image credit: NOAA's Satellite Services Division (SSD).

Now that Dolly is inland, a quick decay is anticipated, and it is possible that the cyclone could dissipate sooner than indicated here. Given the scarcity of surface observations and the fact that the strongest winds are not currently located over any highly populated areas, estimating the intensity of the now inland Dolly is a little difficult. The cloud pattern hasn't changed much since landfall except that the expansive convective canopy has shrunk into a more banded appearance, suggesting that Dolly is likely still somewhere between 35 and 40 kt for now. As the cyclone moves slowly across the mountains, the circulation is liable to spin down rather quickly.

Even after Dolly dissipates, the threat for very heavy rainfall, flash flooding, and mudslides will still be extant, as the mid-level center will be slower to wind down, even over the high mountains.

Tropical storm warnings remain in effect for portions of the coast (see below), but these warnings will likely be dropped with the next advisory as Dolly moves farther inland and weakens.

Intensity forecast

Initial 09/03 0300Z 21.9°N 97.7°W 40 kt 45 mph: inland
12 hour 09/03 1200Z 22.0°N 99.0°W 30 kt 35 mph: inland
24 hour 09/04 0000Z 22.0°N 99.8°W 25 kt 30 mph: post-tropical/remnant low
36 hour 09/04 1200Z: dissipated

Track forecast



Figure 2. My forecast track for Dolly.

NHC storm information


000
WTNT35 KNHC 030235
TCPAT5

BULLETIN
TROPICAL STORM DOLLY ADVISORY NUMBER 6
NWS NATIONAL HURRICANE CENTER MIAMI FL AL052014
1000 PM CDT TUE SEP 02 2014

...CENTER OF DOLLY MOVING ASHORE JUST SOUTH OF TAMPICO
MEXICO...


SUMMARY OF 1000 PM CDT...0300 UTC...INFORMATION
-----------------------------------------------
LOCATION...21.9N 97.7W
ABOUT 25 MI...40 KM SSE OF TAMPICO MEXICO
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...W OR 270 DEGREES AT 9 MPH...15 KM/H
MINIMUM CENTRAL PRESSURE...1002 MB...29.59 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WARNING IS IN EFFECT FOR...
* CABO ROJO TO BOCA DE CATAN

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 1000 PM CDT...0300 UTC...THE CENTER OF TROPICAL STORM DOLLY WAS
LOCATED NEAR LATITUDE 21.9 NORTH...LONGITUDE 97.7 WEST. DOLLY IS
MOVING TOWARD THE WEST NEAR 9 MPH...15 KM/H...AND THIS GENERAL
MOTION IS EXPECTED TO CONTINUE FOR THE NEXT DAY OR SO. ON THE
FORECAST TRACK...THE CENTER OF DOLLY WILL MOVE INLAND OVER
NORTHEASTERN MEXICO THROUGH WEDNESDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 45 MPH...75 KM/H...WITH HIGHER
GUSTS. WEAKENING WILL OCCUR DURING THE NEXT 24 HOURS WHILE DOLLY
MOVES INLAND. THE SYSTEM IS EXPECTED TO DISSIPATE BY WEDNESDAY
NIGHT.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 140 MILES...
220 KM...PRIMARILY TO THE NORTHEAST OF THE CENTER.

THE MINIMUM CENTRAL PRESSURE ESTIMATED FROM AIRCRAFT DATA IS
1002 MB...29.59 INCHES.


HAZARDS AFFECTING LAND
----------------------
RAINFALL...DOLLY IS EXPECTED TO PRODUCE RAINFALL AMOUNTS OF 5 TO 10
INCHES WITH ISOLATED MAXIMUM AMOUNTS OF 15 INCHES ACROSS MUCH OF
TAMAULIPAS AND NUEVO LEON...AS WELL AS NORTHERN VERACRUZ AND EASTERN
SAN LUIS POTOSI MEXICO THROUGH WEDNESDAY EVENING. THIS RAINFALL IS
EXPECTED TO CAUSE LIFE-THREATENING FLASH FLOODS AND MUD SLIDES IN
AREAS OF MOUNTAINOUS TERRAIN.

WIND...TROPICAL STORM CONDITIONS ARE EXPECTED IN PORTIONS OF THE
WARNING AREA THROUGH EARLY WEDNESDAY.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...100 AM CDT.
NEXT COMPLETE ADVISORY...400 AM CDT.

$$
FORECASTER BROWN



Norbert

Tropical Storm Norbert continues to move toward the southern Baja California peninsula. As of the 0300Z NHC advisory, the following information was contained on Norbert:

Wind: 45 mph, with higher gusts
Location: 19.2°N 106.9°W
Movement: NNW at 8 mph
Pressure: 1003 mb

The cloud pattern associated with Norbert is gradually becoming better organized. While there have been no recent microwave passes over the cyclone, the convective pattern noted on conventional satellite imagery gives evidence that Norbert could be developing an inner core, with the center likely just outside the very cold (-70 to -80C) convection possibly presaging the formation of a central dense overcast. The center not being fully under the convection can be explained by modest northerly shear on the backside of a mid-tropospheric ridge over central Mexico, the same one steering Dolly. Recently, the upper-tropospheric outflow has expanded -- more like become existent for the first time, actually -- to the north, implying a decrease in large-scale shear.



Figure 3. Latest infrared satellite image of Tropical Storm Norbert. Image credit: NOAA's Satellite Services Division (SSD).

Other than the shear, environmental conditions appear to favor intensification. Curiously, most of the guidance keeps Norbert below hurricane strength, possibly due to the northern portion of the cyclone interacting with Baja California Sur. My forecast is above all of the guidance, but is closest to the SHIPS, which takes Norbert up to 65 kt in 48 hours. If the cyclone can manage to formulate a cohesive inner core and the shear continues to lessen, rapid intensification would not be a surprise over the next day or so, as Norbert remains over SSTs of about 30C. It should be noted that the GFS and ECMWF keep some shear over Norbert through the next few days, but the ECMWF shows less shear. In about 48 hours, Norbert is likely to make its closest approach to the coast, and depending on how far north it moves, the tropical storm could conceivably be a little weaker than I'm advertising at those times. Subsequent to 48 hours, Norbert is forecast to move across progressively cooler waters and entrain drier air to the west of Baja California Sur, which should lead to a steady decay of the cyclone even though the shear could lessen a bit at the end of the forecast period.

Norbert appears to be following the National Hurricane Center forecast track, although recent satellite data suggests the cyclone could be moving a bit faster than that projection. Water vapor imagery shows that Norbert is wedged between a mid-to upper-level ridge over northern Mexico and a broad mid- to upper-level trough over the northwestern United States. Looking at the GFS and ECMWF 500 mb height fields, this trough is forecast to dive southeastward and amplify as it does so, a solution that appears viable given current trends. The models disagree on how Norbert will respond to this trough, but all of them except the NAVGEM -- which had a faulty initialization of Norbert -- turn the storm poleward. The guidance might perhaps be becoming a bit more stable (hopefully), as the GFS has shifted westward at 0z, closer to the 12z ECMWF solution. This is still dangerously close to southern Baja, however, and interests there should closely monitor the progress of Norbert over the next couple of days. Beyond 48 hours, the models show a ridge rebuilding to the north of Norbert, which should bend the track back to the left a bit before another trough moves into the Pacific Northwest and weakens the ridge. At that point, it is difficult to tell if Norbert will respond to the trough; my guess is a little, as it should still contain 40 to 50 kt winds at that time, but probably not enough to induce a full on northward motion like some of the models are showing. My forecast brings Norbert a little closer to the coast than the NHC prediction does, but still keeps the cyclone about 100 miles offshore.

A tropical storm watch remains in effect for the southern portion of Baja California Sur. Depending on whether or not Norbert moves northward, this could be upgraded to a tropical storm or hurricane warning in subsequent advisories, as noted by the National Hurricane Center. Even if Norbert remains offshore, showery bands with gusty winds and locally heavy rainfall will likely affect coastal and inland areas of the southern Baja Peninsula.

Intensity forecast

Initial 09/03 0300Z 19.2°N 106.9°W 40 kt 45 mph
12 hour 09/03 1200Z 19.7°N 107.5°W 50 kt 60 mph
24 hour 09/04 0000Z 20.5°N 108.3°W 55 kt 65 mph
36 hour 09/04 1200Z 21.3°N 109.1°W 65 kt 75 mph
48 hour 09/05 0000Z 22.0°N 110.0°W 70 kt 80 mph
72 hour 09/06 0000Z 23.1°N 111.5°W 60 kt 70 mph
96 hour 09/07 0000Z 23.9°N 112.9°W 50 kt 60 mph
120 hour 09/08 0000Z 25.3°N 115.3°W 40 kt 45 mph

Track forecast



Figure 4. My forecast track for Norbert.

NHC storm information

000
WTPZ34 KNHC 030239
TCPEP4

BULLETIN
TROPICAL STORM NORBERT ADVISORY NUMBER 3
NWS NATIONAL HURRICANE CENTER MIAMI FL EP142014
800 PM PDT TUE SEP 02 2014

...NORBERT NOW MOVING NORTH-NORTHWESTWARD...
...FORECAST TO STRENGTHEN...


SUMMARY OF 800 PM PDT...0300 UTC...INFORMATION
----------------------------------------------
LOCATION...19.2N 106.9W
ABOUT 115 MI...185 KM SW OF CABO CORRIENTES MEXICO
ABOUT 320 MI...515 KM SE OF THE SOUTHERN TIP OF BAJA CALIFORNIA
MAXIMUM SUSTAINED WINDS...45 MPH...75 KM/H
PRESENT MOVEMENT...NNW OR 330 DEGREES AT 8 MPH...13 KM/H
MINIMUM CENTRAL PRESSURE...1003 MB...29.62 INCHES


WATCHES AND WARNINGS
--------------------
CHANGES WITH THIS ADVISORY...

NONE.

SUMMARY OF WATCHES AND WARNINGS IN EFFECT...

A TROPICAL STORM WATCH IS IN EFFECT FOR...
* LA PAZ TO SANTA FE MEXICO

A TROPICAL STORM WATCH MEANS THAT TROPICAL STORM CONDITIONS ARE
POSSIBLE WITHIN THE WATCH AREA...GENERALLY WITHIN 48 HOURS.

FOR STORM INFORMATION SPECIFIC TO YOUR AREA...PLEASE MONITOR
PRODUCTS ISSUED BY YOUR NATIONAL METEOROLOGICAL SERVICE.


DISCUSSION AND 48-HOUR OUTLOOK
------------------------------
AT 800 PM PDT...0300 UTC...THE CENTER OF TROPICAL STORM NORBERT WAS
LOCATED NEAR LATITUDE 19.2 NORTH...LONGITUDE 106.9 WEST. NORBERT IS
MOVING TOWARD THE NORTH-NORTHWEST NEAR 8 MPH...13 KM/H. A TURN
TOWARD THE NORTHWEST IS EXPECTED OVERNIGHT...AND A GENERAL
NORTHWESTWARD MOTION IS EXPECTED TO CONTINUE THROUGH THURSDAY. ON
THE FORECAST TRACK...THE CENTER OF NORBERT IS EXPECTED TO MOVE AWAY
FROM THE SOUTHWESTERN COAST OF MEXICO OVERNIGHT...AND APPROACH THE
SOUTHERN TIP OF THE BAJA CALIFORNIA PENINSULA ON THURSDAY.

MAXIMUM SUSTAINED WINDS ARE NEAR 45 MPH...75 KM/H...WITH HIGHER
GUSTS. STRENGTHENING IS FORECAST DURING THE NEXT 48 HOURS...AND
NORBERT IS EXPECTED TO REACH HURRICANE STRENGTH ON THURSDAY.

TROPICAL STORM FORCE WINDS EXTEND OUTWARD UP TO 60 MILES...95 KM
FROM THE CENTER.

THE ESTIMATED MINIMUM CENTRAL PRESSURE IS 1003 MB...29.62 INCHES.


HAZARDS AFFECTING LAND
----------------------
WIND...TROPICAL STORM CONDITIONS ARE POSSIBLE WITHIN THE WATCH AREA
BY THURSDAY AFTERNOON.

RAINFALL...NORBERT IS EXPECTED TO PRODUCE RAINFALL AMOUNTS OF 2 TO
4 INCHES OVER COLIMA AND WESTERN PARTS OF MICHOACAN AND JALISCO IN
SOUTHWESTERN MEXICO THROUGH WEDNESDAY.


NEXT ADVISORY
-------------
NEXT INTERMEDIATE ADVISORY...1100 PM PDT.
NEXT COMPLETE ADVISORY...200 AM PDT.

$$
FORECASTER BRENNAN

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About KoritheMan

I'm just a 23 year old with an ardent passion for weather. I first became aware of this interest after Tropical Storm Isidore struck my area in 2002.

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