Typescript – Resolve “Property does not exist on type ‘Vue'” error

I am using Typescript with Vuejs to build an application. I have several stand alone components (.vue) files that I am importing into a Typescript (.ts) file. In the Typescript file, I am importing Vue from the npm Vue library and then creating a new Vue to display my components. The error that I am seeing is:

Property x does not exist on type 'Vue'

My build system is Webpack with tsc. Why am I getting this error and how can I resolve it?

main.ts

import Vue from 'vue';
import Competency from '../components/competency.vue';

new Vue({
  el: "#app",
  components: {
    'competency': Competency
  },
  data:{
    count: 0
  },
  methods:{
    initialize: function(){
      this.count = count + 1; // Errors here with Property count does not exist on type vue
    }
  }
})

tsconfig

{
  "compilerOptions": {
    // "allowJs": true,
    "allowSyntheticDefaultImports": true,
    "experimentalDecorators": true,
    "lib": [
      "es2015",
      "dom",
      "es2015.promise"
    ],
    "module": "es2015",
    "moduleResolution": "node",
    "noEmitOnError": true,
    "noImplicitAny": false,
    //"outDir": "./build/",
    "removeComments": false,
    "sourceMap": true,
    "target": "es5"

  },
  "exclude": [
    "./node_modules",
    "wwwroot",
    "./Model"
  ],
  "include": [
    "./CCSEQ",
    "./WebResources"
  ]
}

webpack.config.js

const path = require('path');
const webpack = require('webpack');
const HtmlWebpackPlugin = require('html-webpack-plugin');
const CleanWebpackPlugin = require('clean-webpack-plugin');

module.exports = {
    entry: {
        Evaluations: './WebResources/js/main.ts'
    },
    devServer: {
        contentBase: './dist'
    },
    module: {
        rules: [{
                test: /\.ts$/,
                exclude: /node_modules|vue\/src/,
                loader: 'ts-loader',
                exclude: /node_modules/,
                options: {
                    appendTsSuffixTo: [/\.vue$/]
                }
            },
            {
                test: /\.vue$/,
                loader: 'vue-loader',
                options: {
                    esModule: true
                }
            },
            {
                test: /\.css$/,
                use: [
                    'style-loader',
                    'css-loader'
                ]
            },
            {
                test: /\.(png|svg|jpg|gif)$/,
                use: [
                    'file-loader'
                ]
            },
        ]
    },
    resolve: {
        extensions: [".tsx", ".ts", ".js"],
        alias: {
            'vue$': 'vue/dist/vue.esm.js'
        }
    },
    plugins: [
        new CleanWebpackPlugin(['dist']),
        new HtmlWebpackPlugin({
            filename: 'Evaluations.html',
            template: './WebResources/html/Evaluations.html'
        }), new HtmlWebpackPlugin({
            filename: 'ExpenseUpload.html',
            template: './WebResources/html/ExpenseUpload.html'
        }), new webpack.optimize.CommonsChunkPlugin({
            name: 'WebAPI'
        })
    ],
    output: {
        filename: '[name].bundle.js',
        path: path.resolve(__dirname, 'dist')
    }
}