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Tropical Storm MARTY Forecast Discussion Number 11

2015-09-29 10:37:40| Tropical Depression LIDIA

Issued at 400 AM CDT TUE SEP 29 2015

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Tropical Storm JOAQUIN Forecast Discussion Number 6

2015-09-29 10:37:11| National Hurricane Center (Atlantic)

Issued at 500 AM EDT TUE SEP 29 2015 000 WTNT41 KNHC 290837 TCDAT1 TROPICAL STORM JOAQUIN DISCUSSION NUMBER 6 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015 500 AM EDT TUE SEP 29 2015 The low-level center of Joaquin remains exposed on the northwestern edge of the deep convection due to about 20 kt of shear. A pair of ASCAT passes around 01-02Z showed peak winds of around 35 kt, and that remains the intensity for this advisory, in agreement with the latest TAFB and SAB Dvorak estimates. The ASCAT data were also used to adjust the initial 34-kt wind radii. After moving quickly southwestward earlier, the center of Joaquin appears to be moving more slowly westward at about 4 kt. The track forecast remains highly uncertain, and if anything, the spread in the track model guidance is larger now beyond 48 hours due to uncertainty in the evolution of the synoptic-scale flow and the structure of Joaquin. In particular, the global models are having trouble with the evolution of a deep layer trough over the southeastern U.S. late in the forecast period, with added uncertainty about the structure of Joaquin and how it might interact with the trough. The latest runs of the UKMET and ECMWF bring Joaquin farther southwest early in the period and then show a northward and northeastward motion, respectively, ahead of the trough at days 4 and 5. The GFS shows a weaker Joaquin being absorbed into a frontal zone off the U.S. east coast in 3 to 4 days, while the HWRF and GFDL continue to show a faster northward and then northwestward track. In the first 48 hours, the new NHC track is a little to the south of the previous one accounting for the initial position and motion and a trend toward the multi-model consensus. At days 3 through 5, the official forecast is a little to the right of and slower than the previous one given the large spread in the track guidance. Needless to say, confidence in the details of the track forecast, especially beyond 48 hours, is extremely low. The SHIPS model output shows moderate to strong northerly shear continuing over the cyclone for the next 24 to 36 hours, which should only allow for slow strengthening. After that time, the shear decreases a bit and the cyclone could strengthen a little more while over warm waters. However, there is a lot of spread in the intensity guidance as well. As noted above, the latest run of the GFS dissipates Joaquin in 3 to 4 days. On the other hand, the ECMWF and UKMET show the cyclone deepening considerably in the short term, while the HWRF and GFDL show more strengthening later in the period. Given the uncertainty in Joaquin's structure and track, the new NHC forecast remains conservative, and is closest to the SHIPS model and below the intensity consensus. FORECAST POSITIONS AND MAX WINDS INIT 29/0900Z 26.6N 70.6W 35 KT 40 MPH 12H 29/1800Z 26.6N 71.3W 40 KT 45 MPH 24H 30/0600Z 26.7N 72.2W 40 KT 45 MPH 36H 30/1800Z 26.8N 72.8W 45 KT 50 MPH 48H 01/0600Z 27.1N 73.2W 50 KT 60 MPH 72H 02/0600Z 28.5N 73.5W 55 KT 65 MPH 96H 03/0600Z 32.0N 73.0W 55 KT 65 MPH 120H 04/0600Z 36.5N 73.0W 55 KT 65 MPH $$ Forecaster Brennan

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Hurricane MARTY Forecast Discussion Number 10

2015-09-29 04:37:40| Tropical Depression LIDIA

Issued at 1000 PM CDT MON SEP 28 2015

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Tropical Storm JOAQUIN Forecast Discussion Number 5

2015-09-29 04:37:08| National Hurricane Center (Atlantic)

Issued at 1100 PM EDT MON SEP 28 2015 000 WTNT41 KNHC 290237 TCDAT1 TROPICAL STORM JOAQUIN DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015 1100 PM EDT MON SEP 28 2015 Satellite images indicate that the shower and thunderstorm activity associated with the depression has increased and become better organized during the past several hours. In addition, the low-level center now appears to have moved closer to the convection than it was earlier. The latest Dvorak classifications from TAFB and SAB were 2.5/35 kt, and the initial intensity is set at that value, making the cyclone Tropical Storm Joaquin. This intensity analysis also agrees with the reconnaissance aircraft data from earlier today that showed winds just under tropical-storm force. The center of Joaquin has been moving southwestward during the last several hours, but it is expected to begin moving slowly westward overnight. This westward track is forecast to continue for a couple of days while a mid-level ridge remains to the north of the storm. After that time, a trough is anticipated to amplify over the eastern United States, which should cause Joaquin to turn northward and accelerate. There is considerable spread in the models, mainly due to the timing of when and how fast the storm makes the northward turn, due to differences in the evolution of the trough. In general, the guidance envelope has shifted southward for the first couple of days and then westward after that time. The official track forecast has been adjusted accordingly, but additional southward and westward adjustment may be needed in subsequent advisories. Northwesterly shear of about 20 kt is currently affecting Joaquin, causing most of the thunderstorm activity to be located to the southeast of the center. The shear is expected to lessen some during the next couple of days, which in combination with warm water and high relative humidity values should allow Joaquin to strengthen. The official intensity forecast is raised from the previous one, but is lower than the intensity model consensus at days 3-5. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 26.7N 70.4W 35 KT 40 MPH 12H 29/1200Z 26.9N 71.0W 40 KT 45 MPH 24H 30/0000Z 27.1N 72.0W 40 KT 45 MPH 36H 30/1200Z 27.2N 72.8W 45 KT 50 MPH 48H 01/0000Z 27.4N 73.4W 50 KT 60 MPH 72H 02/0000Z 28.6N 74.0W 55 KT 65 MPH 96H 03/0000Z 32.4N 74.0W 55 KT 65 MPH 120H 04/0000Z 38.0N 74.0W 55 KT 65 MPH $$ Forecaster Cangialosi

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Tropical Depression ELEVEN Forecast Discussion Number 4

2015-09-28 22:45:57| National Hurricane Center (Atlantic)

Issued at 500 PM EDT MON SEP 28 2015 000 WTNT41 KNHC 282045 TCDAT1 TROPICAL DEPRESSION ELEVEN DISCUSSION NUMBER 4 NWS NATIONAL HURRICANE CENTER MIAMI FL AL112015 ISSUED BY THE NWS WEATHER PREDICTION CENTER COLLEGE PARK MD 500 PM EDT MON SEP 28 2015 The low-level center has become well exposed due to continued northwesterly shear of 20 kt or more, with the mid-level center displaced well to the southeast of the low-level center. Flight-level and SFMR-observed wind data from an Air Force reconnaissance aircraft showed that the maximum winds remain near 30 kt. This is also consistent with the latest Dvorak estimates from SAB and TAFB. The center of the depression has been moving well to the left of the previous track, with the initial motion estimated to be 270/05 kt. In addition to the more westward initial motion, there have been significant changes in the model guidance, with the latest ECMWF forecast taking the cyclone much farther south and west than the GFS in 3-5 days. This appears to be the result of enhanced mid-level ridging to the north of the cyclone in the ECMWF at that time frame. This has necessitated a significant southwestward shift of the official forecast, although for continuity the new NHC track does not take the cyclone as far to the southwest as the ECMWF. Given the large spread now seen in the dynamical track guidance, confidence in the track forecast is rather low. The strong shear over the system is likely to continue for at least the next 12-24 hours and given the large displacement between the low- and mid-level centers, no intensification is anticipated in the short term. The dynamical guidance indicates some relaxation of the shear in a day or two, so the official forecast shows the cyclone strengthening into a tropical storm later on Tuesday. This is close to the intensity model consensus through 48 hours, and a little below it thereafter. Given the large uncertainty in the track forecast, there is also uncertainty as to what kind of environment the cyclone will encounter during the forecast period, which also leads to low confidence in the official intensity forecast. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 27.5N 70.2W 30 KT 35 MPH 12H 29/0600Z 27.7N 71.0W 30 KT 35 MPH 24H 29/1800Z 27.9N 72.0W 35 KT 40 MPH 36H 30/0600Z 28.3N 72.8W 40 KT 45 MPH 48H 30/1800Z 28.6N 73.4W 45 KT 50 MPH 72H 01/1800Z 30.0N 74.0W 45 KT 50 MPH 96H 02/1800Z 33.0N 74.0W 45 KT 50 MPH 120H 03/1800Z 38.5N 73.5W 45 KT 50 MPH $$ Forecaster Pasch/Hayes

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