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Hurricane LESTER Forecast Discussion Number 18

2016-08-29 04:52:40| National Hurricane Center (East Pacific)

Issued at 800 PM PDT SUN AUG 28 2016 000 WTPZ43 KNHC 290252 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 18 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 800 PM PDT SUN AUG 28 2016 After appearing steady state throughout the day, the cloud pattern of Lester has become a little better organized during the past couple of hours with an eye apparent once again in satellite images. The initial wind speed is held at 75 kt for this advisory, in agreement with the Dvorak classifications from TAFB and SAB, but this could be a little conservative. The environmental parameters for intensification are mixed. Although the shear is expected to be light to moderate during the next several days, marginally warm sea surface temperatures and intrusions of dry air could negate the influence of the low shear. Based on the current trend and expected conditions, some slight strengthening is shown in the short term followed by a very slow weakening thereafter. This forecast is in close agreement with the intensity model consensus and is not too different from the previous NHC forecast. The hurricane is moving westward about 12 kt on the south side of a strong high pressure system. Lester is expected to remain to the south of mid-level ridging during the next several days, and that should keep the system moving westward at about the same forward speed. The model guidance is in good agreement, and only small changes were made to the previous NHC track prediction. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 17.9N 126.4W 75 KT 85 MPH 12H 29/1200Z 18.0N 128.4W 80 KT 90 MPH 24H 30/0000Z 18.1N 131.1W 80 KT 90 MPH 36H 30/1200Z 18.2N 133.6W 75 KT 85 MPH 48H 31/0000Z 18.2N 136.1W 75 KT 85 MPH 72H 01/0000Z 18.1N 140.6W 75 KT 85 MPH 96H 02/0000Z 18.5N 145.3W 75 KT 85 MPH 120H 03/0000Z 19.7N 150.0W 70 KT 80 MPH $$ Forecaster Cangialosi

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Hurricane GASTON Forecast Discussion Number 26

2016-08-29 04:50:34| National Hurricane Center (Atlantic)

Issued at 1100 PM AST SUN AUG 28 2016 000 WTNT42 KNHC 290250 TCDAT2 HURRICANE GASTON DISCUSSION NUMBER 26 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 1100 PM AST SUN AUG 28 2016 Gaston remains a well organized hurricane. Satellite images indicate that the eye remains quite distinct with a symmetric ring of deep convection around it. The upper-level outflow is well established both to the west and the east of the system. The latest Dvorak classifications from TAFB and SAB are 5.5/102 kt, and automated values from CIMSS at the University of Wisconsin are 5.9/112 kt. Based on these data, the initial wind speed is nudged upward to 105 kt. Gaston has not moved very little during the last several hours. A continued slow and likely erratic northward motion is forecast overnight and Monday while Gaston remains in weak steering currents caused by a blocking mid-level ridge to its northwest. A trough that is currently over eastern Canada is expected to dampen by the time it nears Gaston, but it should be strong enough to erode the ridge and allow the hurricane to become embedded in the mid-latitude westerlies. This pattern change should result in Gaston's turning east-northeastward in about 24 hours, with the cyclone continuing in that direction through the remainder of the forecast period. The model guidance remains tightly packed, and little change was made to the previous NHC track prediction. The atmospheric conditions suggest that Gaston could maintain its strength for the next day or so, however, given the expected slow motion of the cyclone there is some chance that cold water upwelling would counteract that. Beyond that time, the hurricane is likely to encounter an environment of increasing shear, drier air, and cooler water. Given these expected conditions, the NHC intensity forecast shows a gradual weakening trend beginning on Monday. This prediction is in best agreement with the SHIPS guidance. FORECAST POSITIONS AND MAX WINDS INIT 29/0300Z 30.6N 55.2W 105 KT 120 MPH 12H 29/1200Z 30.9N 55.4W 105 KT 120 MPH 24H 30/0000Z 31.4N 54.9W 100 KT 115 MPH 36H 30/1200Z 32.1N 53.5W 95 KT 110 MPH 48H 31/0000Z 33.0N 51.5W 95 KT 110 MPH 72H 01/0000Z 35.5N 46.0W 90 KT 105 MPH 96H 02/0000Z 37.4N 38.7W 75 KT 85 MPH 120H 03/0000Z 37.7N 33.0W 60 KT 70 MPH $$ Forecaster Cangialosi

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Tropical Depression NINE Forecast Discussion Number 1

2016-08-28 22:56:30| National Hurricane Center (Atlantic)

Issued at 500 PM EDT SUN AUG 28 2016 000 WTNT44 KNHC 282055 TCDAT4 TROPICAL DEPRESSION NINE DISCUSSION NUMBER 1 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092016 500 PM EDT SUN AUG 28 2016 Data from a NOAA Hurricane Hunter aircraft indicate that the area of low pressure located in the Florida Straits now has a well-defined center. Satellite imagery shows a significant increase in the convective organization today, and as a result the system is now classified as a tropical cyclone. The initial intensity is set to 30 kt based on the highest believable wind data from the aircraft, which reported a central pressure of 1009 mb. The depression will be moving through a marginal environment for intensification during the next day or so, with vertical shear of 15 to 20 kt. As a result only slow strengthening is expected in the short term. Later on, the environment may improve a little as the shear is forecast to decrease somewhat and become southwesterly, which should allow for a little more strengthening. However, there are mixed signals in the model guidance, with the ECMWF now showing the cyclone dissipating in the Gulf, while the GFS delays development until 4-5 days. Much of the tropical cyclone guidance is more aggressive. Given this uncertainty, the NHC intensity forecast is quite conservative and shows the system peaking at 45 kt, below all the explicit intensity guidance in consideration of the negative signal from the ECMWF. Needless to say, the confidence in the intensity forecast is even lower than usual for this system. The initial motion estimate is an uncertain 270/09 given the recent formation of the center. The cyclone will be steered in the short range by a mid-level ridge centered over the southeastern United States. This ridge will weaken in 2-3 days, which will cause the cyclone to slow down and turn northward during this time. Late in the period a northeastward acceleration is expected ahead of an approaching mid-latitude trough. There is reasonable agreement in the track of the cyclone in the global model guidance, although there is a fair bit of along-track spread late in the period. The NHC forecast is close to a consensus of the GFS and ECMWF through day 4 and is a little faster than the GFS and GEFS ensemble mean at day 5. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 23.7N 81.7W 30 KT 35 MPH 12H 29/0600Z 23.9N 83.6W 30 KT 35 MPH 24H 29/1800Z 24.3N 85.4W 35 KT 40 MPH 36H 30/0600Z 24.6N 86.8W 35 KT 40 MPH 48H 30/1800Z 25.1N 87.6W 40 KT 45 MPH 72H 31/1800Z 26.8N 87.4W 45 KT 50 MPH 96H 01/1800Z 29.0N 84.5W 45 KT 50 MPH 120H 02/1800Z 31.0N 80.0W 45 KT 50 MPH $$ Forecaster Brennan

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Hurricane LESTER Forecast Discussion Number 17

2016-08-28 22:36:10| National Hurricane Center (East Pacific)

Issued at 200 PM PDT SUN AUG 28 2016 000 WTPZ43 KNHC 282035 TCDEP3 HURRICANE LESTER DISCUSSION NUMBER 17 NWS NATIONAL HURRICANE CENTER MIAMI FL EP132016 200 PM PDT SUN AUG 28 2016 The cloud pattern has not changed very much during the day and the convection has been fluctuating in intensity. Occasionally, an eye feature has been observed on conventional imagery. Dvorak estimates, both objective and subjective, have not changed since this morning and still support an initial intensity of 75 kt. The shear environment appears to be favorable for Lester to intensify, but SSTs along the hurricane track are decreasing slightly. Given these two opposing factors, the NHC forecast calls for no change in intensity during the next 5 days. This forecast follows very closely the intensity consensus model. Lester is moving westward or 270 degrees at 11 kt. The hurricane is embedded within a deep layer of easterly flow on the south side of a persistent subtropical ridge across the Pacific. Given the well established steering flow, the track guidance continues to be tightly packed, and this increases the confidence in the future motion of the hurricane. The NHC forecast is very similar to the previous one and is basically on top of the multi-model consensus TVCN. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 17.8N 124.7W 75 KT 85 MPH 12H 29/0600Z 17.8N 126.6W 75 KT 85 MPH 24H 29/1800Z 18.0N 129.5W 75 KT 85 MPH 36H 30/0600Z 18.0N 132.0W 75 KT 85 MPH 48H 30/1800Z 18.0N 134.5W 75 KT 85 MPH 72H 31/1800Z 18.0N 139.0W 75 KT 85 MPH 96H 01/1800Z 18.5N 143.5W 75 KT 85 MPH 120H 02/1800Z 19.5N 148.0W 70 KT 80 MPH $$ Forecaster Avila

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Hurricane GASTON Forecast Discussion Number 25

2016-08-28 22:35:08| National Hurricane Center (Atlantic)

Issued at 500 PM AST SUN AUG 28 2016 000 WTNT42 KNHC 282034 TCDAT2 HURRICANE GASTON DISCUSSION NUMBER 25 NWS NATIONAL HURRICANE CENTER MIAMI FL AL072016 500 PM AST SUN AUG 28 2016 The 15 n mi diameter eye has become more distinct on visible satellite images today, and enhanced IR images show a cooling of the cloud tops surrounding the eye. These features indicate strengthening, and the current intensity is increased to 100 kt in agreement with the subjective Dvorak estimates from TAFB and SAB, as well as objective ADT numbers from UW-CIMSS. Upper-level outflow is well-established both to the west and the east of the hurricane. Based on a consensus of the intensity models, not much additional strengthening is anticipated. When Gaston moves to a little higher latitude, westerly shear on the system should increase, and steady weakening is expected to commence in about 48 hours. Gaston continues to crawl northwestward while being partially blocked by a narrow mid-level subtropical ridge. The hurricane is forecast to work its way through the ridge over the next day or so. By Tuesday, an east-northeastward motion with gradual acceleration is likely as the system begins to feel the effect of the mid-latitude westerlies. The official forecast track is shifted a little southward late in the forecast period, in line with the latest global model guidance. FORECAST POSITIONS AND MAX WINDS INIT 28/2100Z 30.8N 55.1W 100 KT 115 MPH 12H 29/0600Z 31.0N 55.5W 100 KT 115 MPH 24H 29/1800Z 31.4N 55.5W 100 KT 115 MPH 36H 30/0600Z 32.0N 54.4W 95 KT 110 MPH 48H 30/1800Z 32.8N 52.6W 95 KT 110 MPH 72H 31/1800Z 34.9N 47.7W 85 KT 100 MPH 96H 01/1800Z 37.5N 40.5W 75 KT 85 MPH 120H 02/1800Z 37.5N 33.5W 60 KT 70 MPH $$ Forecaster Pasch

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